System for Removal of Metals from Aqueous Solutions

ABSTRACT

System and method for removal of metals from aqueous solutions. Contactors for contacting aqueous solutions are formed of sorbents of metal oxides processed from metal containing solutions. Metal containing solutions are mixed with heated aqueous oxidizing solutions and processed in a continuous process reactor or batch processing system. Combinations of temperature, pressure, molarity, Eh value, and pH value of the mixed solution are monitored and adjusted so as to maintain solution conditions within a desired stability area during processing. This results in metal oxides having high or increased pollutant loading capacities and/or oxidation states. Contactors formed of sorbents processed according to processes of the invention capture or removing target pollutants from drinking water or other residential or industrial aqueous streams.

CROSS-REFERENCE TO RELATED APPLICATIONS

This divisional application claims priority to the benefit of U.S.patent application Ser. No. 10/902,439, filed Jul. 28, 2004, whichclaims priority to U.S. Provisional Application Nos. 60/491,653, filedJul. 31, 2003; U.S. Provisional Application No. 60/538,386 filed Jan.21, 2004; 60/538,644 filed Jan. 22, 2004; 60/538,968 filed Jan. 23,2004; 60/549,255 filed Mar. 2, 2004; and U.S. patent application Ser.No. 10/767,460 filed Jan. 28, 2004 and patented on Sep. 2, 2008 as U.S.Pat. No. 7,419,637, which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to systems and processes for preparing andregenerating metal oxide compounds and to the use of such compounds assorbents, filtration media, and/or purification media for removal ofpollutants from gases, including industrial and waste gas streams, andaqueous streams, including drinking water and industrial water streams.

BACKGROUND OF THE INVENTION

Metal oxides are utilized for a number of applications, such as gaseousand aqueous pollution control systems, steel manufacture, batteries andcatalytic converters, to name a few. Of particular, but not exclusive,interest to Applicants is the use of oxides of manganese in airpollution control systems, water filtration, and respiratorapplications. Applicants are co-inventors of the subject matter ofissued U.S. Pat. Nos. 6,579,507 and 6,610,263, the disclosures of whichare incorporated herein by reference. These patents disclose pollutantremoval systems and processes, sometimes referred to as Pahlman Process™Technology, which utilize dry and wet removal techniques andcombinations thereof, incorporating the use of oxides of manganese as asorbent for capture and removal of target pollutants from gas streams.

Metal oxides have the ability to capture target pollutants from gasstreams; however, the low pollutant loading rates achieved with variousprior art metal oxides have made some industrial applications of thisattribute uneconomical. The low target pollutant loading rates ofvarious prior art metal oxide sorbents would require voluminous amountsof sorbent to effectively capture large quantities of target pollutantsthat exist at many industrial sites, e.g., NO_(X) and/or SO₂. The largequantity of sorbent that would be required to capture NO_(X) and/or SO₂could result in an overly costly pollutant removal system, sorbentregeneration system, and waste removal system. It would therefore bedesirable to enhance the loading capacities of the metal oxide sorbentin order to economically implement a pollution removal system utilizingmetal oxide sorbents.

Metal oxides are also useful in removing pollutants from aqueousstreams. However, limitations of prior art metal oxides again result indisappointing pollutant removal performance and marginal economicreturn. As an example, arsenic is found in water in two common forms orspecies, arsenite (As⁺³) and arsenate (As⁺⁵). Metal oxides ofconventional systems have difficulty in removing arsenite, and costlyprovisions are often necessary to oxidize the arsenite to arsenate thatmay be more easily removed. Further, Applicants are not aware of anycurrent technology that can remove arsenite and/or arsenate along withselectively removing hardness in the form of calcium, magnesium, and/orother hardness minerals.

Personal protective respirators also use metal oxides, amongst othermaterials, in filter elements to capture pollutants and toxins presentin various environments to reduce human exposure risks and concerns.Sorbents and filtration media used in conventional filter elements mayhave a low affinity for certain pollutants requiring more media toensure removal of pollutants to safe levels. These conventional mediamay also have low loading capacities that require frequent replacementof the filter cartridge media to prevent breakthrough of the pollutantor toxin.

Metal oxides processed according to the various embodiments of themethods of the invention may exhibit high loading capacities and/oroxidation potential, may be useful as sorbents or filtration media forremoval of pollutants from gaseous and aqueous process streams, or maybe used to remove arsenite and/or arsenate as well as hardness fromaqueous streams, or may be used as filter media in respirators.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block flow diagram of a system and process according to theinvention.

FIG. 2 is a block flow diagram of a system and process according to theinvention.

FIG. 3 is a block flow diagram of a system and process according to theinvention.

FIG. 4 is a block flow diagram of a system and process according to theinvention.

FIG. 5 is a block flow diagram of a system and process according to theinvention.

FIG. 6 is a block flow diagram of a system and process according to theinvention.

FIG. 7 is a block flow diagram of system and process according to theinvention with electronic controls.

FIG. 8 is a block flow diagram of system and process according to theinvention with electronic controls.

FIG. 9 is a block flow diagram of system and process according to theinvention with electronic controls.

FIG. 10 is a block flow diagram of an electrolytic cell by-productsproduction system and process according to the invention.

FIG. 11 is a Pourbaix diagram for a manganese-water system of 1mole/liter manganese ion concentration.

FIG. 12 is a Pourbaix diagram for a manganese-water system of 10−6mole/liter manganese ion concentration.

FIG. 13 is a Pourbaix diagram for an iron-water system.

FIG. 14 is a Pourbaix diagram for a manganese-iron-water system.

FIG. 15 is a Pourbaix diagram for a manganese-water system.

FIG. 16 is a Pourbaix diagram for a manganese-water system.

FIG. 17 is a Pourbaix diagram for a manganese-water system.

SUMMARY OF THE INVENTION

The invention relates to methods and systems and processes forprocessing metal oxides that, amongst other uses, are utilized as asorbent for removal of target pollutants from a gas or aqueous stream.The metal oxides processed in embodiments of the methods and systems ofthe invention exhibit high pollutant loading capacities and/or oxidationstates. The invention further relates to metal oxides produced by themethods and systems of the invention and novel applications for thesemetal oxides.

In an embodiment of the invention a system for the removal of metalsfrom an aqueous solution comprises a contactor adapted for contacting anaqueous solution containing at least one target pollutant with asorbent, wherein the sorbent removes at least a portion of said targetpollutant from said aqueous stream, said sorbent material comprisingmetal oxides formed by the process of; a) mixing a metal containingsolution and an aqueous oxidizing solution in a sorbent productionreactor to form a solution mixture, the heated aqueous oxidizingsolution being prepared so as to have Eh and pH values within apolyatomic ion stability area, metal ion stability area, a metal oxidestability area, or a co-precipitation stability area of an aqueoussolution at process temperature and process pressure when the aqueousoxidizing solution is mixed with the metal containing solution; b)monitoring and adjusting the temperature, Eh value and pH value of thesolution mixture so as to rapidly move mixture conditions into and tomaintain them within the metal oxide stability area or co-precipitationstability area; and c) maintaining the solution conditions within themetal oxide stability area or co-precipitation stability area so as toproduce metal oxides having high loading capacities and/or high averageoxidation states.

In yet another embodiment of the invention a system for the removal ofpollutants from an aqueous solution comprises a contactor adapted forcontacting an aqueous solution containing at least one target pollutantwith a sorbent, wherein the sorbent removes at least a portion of thetarget pollutant from the aqueous stream, said sorbent comprising ametal oxide formed by the process of; a) providing a metal containingsolution; b) providing a aqueous oxidizing solution, the oxidizingsolution being prepared to have Eh and pH values within a polyatomic ionstability area, metal ion stability area, a metal oxide stability area,or a co-precipitation stability area or to move solution conditionsinitially into the polyatomic ion stability area, metal ion stabilityarea, metal oxide stability area, or co-precipitation stability areawhen contacted with the metal containing solution; c) feeding the metalcontaining solution and the aqueous oxidizing solution into at least onecontinuous flow reactor, the solutions being fed either separately intothe continuous flow reactor where they mix to form a combined mixedprocessing solution or being premixed and fed as a combined mixedprocessing solution; d) heating the combined mixed processing solutionto process temperature; e) monitoring and adjusting combined mixedprocessing solution temperature, Eh value, pH value, molarity, andpressure within the continuous flow reactor so as to rapidly andadaptively move combined mixed processing solution conditions into andmaintain processing solution conditions within the metal oxide stabilityarea or co-precipitation stability area; and f) maintaining combinedmixed processing solution conditions within the metal oxide stabilityarea or co-precipitation stability area as the combined mixed processingsolution travels through the continuous flow reactor so as to producemetal oxides with high loading capacities and/or high average oxidationstates.

Embodiments of the invention may also include a contactor that includesa diffuser for creating a fluidized bed of sorbent and a clear wateroverflow for allowing removal of the aqueous stream once at least aportion of a target pollutant has been removed.

Embodiments of the invention may also include a contactor that includesa diffuser for creating a fluidized bed of sorbent, a clear wateroverflow for allowing removal of the aqueous stream once at least aportion of a target pollutant has been removed, and a reacted sorbentoutlet in the fluidized bed portion of the contactor.

Embodiments of the invention may also include a contactor that includesa diffuser for creating a fluidized bed of sorbent, a clear wateroverflow for allowing removal of the aqueous stream with at least aportion of a target pollutant removed, and a recycle stream forcontrolling velocity through the diffuser.

Embodiments of the invention may also include a contactor that includessorbent that has been precipitated on an active or inactive substrate,sorbent comprising co-precipitated metal oxides, and sorbent includingone or more integrated foreign cations.

In a further embodiment of the invention a system for removal of metalsfrom an aqueous solution is provided. The system of this embodimentcomprised a contactor formed of a metal oxide containing sorbent. Thesystem is configured to bring the aqueous solution into contact with thesorbent. The sorbent comprises regenerable oxides of manganese definedby the formula MnO_(X), where X is about 1.5 to about 2.0, and having aBET value ranging from about 1 to 1000 m²/gram and a particle sizeranging from about 0.5 to about 500 microns.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following definition will be useful in understanding the variousembodiments of the invention disclosed herein.

“Metal oxide stability area” or “stability area,” as used herein, refersto the region of thermodynamic stability for metal oxides at theirvalence states delineated by Eh and pH values for aqueous solutions(also referred to as a “metal-water system”) at specified temperatures,pressures and molarities or, phrased alternatively, the domain of metaloxide stability for an aqueous solution. More specifically, it refers tothe region or domain delineated by Eh and pH values for aqueoussolutions at specified temperatures, pressures and molarities in anelectrochemical stability diagram, such as presented by Pourbaixdiagrams and their equivalents, such as the Latimer Diagram or the FrostDiagram.

“Metal nitrates,” as used herein, refers to and includes the variousforms of metal nitrate compounds, regardless of chemical formula, thatmay be formed through the chemical reaction between NO_(X) and a metaloxide sorbent and includes hydrated forms as well.

“Metal sulfates,” as used herein, refers to and includes the variousforms of metal sulfate compounds, regardless of chemical formula thatmay be formed through the chemical reaction between SO_(X) and a metaloxide sorbent and includes hydrated forms as well.

“MnO₂ stability area,” as used herein, refers to the metal oxidestability area for MnO₂.

“Other metal oxide stability area,” as used herein, refers to the metaloxide stability area of a second metal that may be co-precipitated witha first metal.

“Co-precipitation stability area,” as used herein, refers to a metaloxide stability area corresponding to the area of overlap orintersection between a metal oxide stability area of a first metal and ametal oxide stability area of one or more other metal oxides that are tobe co-precipitated.

“Polyatomic ion stability area,” as used herein, refers to the stabilityarea of a metal containing polyatomic ion.

“Permanganate stability area,” as used herein, refers to the stabilityarea for the permanganate anion, represented by the formula yMnOx*zH₂Owhere y is foreign cation.

“Metal ion stability area,” as used herein, refers to the stability areaof a metal cation.

“Manganese ion stability area,” as used herein, refers to the stabilityarea for the manganese cation.

“Foreign cations” or “foreign metal cations,” as used herein refers tocations of secondary metals, or of non-metal cations.

“Regenerated metal oxides,” as used herein, refers to loaded or reactedmetal oxides that have been processed according to the methods of theinvention in which a heated aqueous oxidizing solution is mixed with aheated slurry of loaded metal oxides (with or without a preoxidationrinse) to form a mixture or a heated aqueous oxidizing solution to whichloaded metal oxides are added (with or without a preoxidation rinse) tofrom a slurry mixture, the mixtures being adjusted and maintained so asto be within the metal oxide stability area.

“Pretreated metal oxides,” as used herein, refers to virgin or unreactedmetal oxides that have been processed according to the methods of theinvention in which a heated aqueous oxidizing solution is mixed with aheated slurry of virgin metal oxides to form a mixture or a heatedaqueous oxidizing solution to which virgin metal oxides are added tofrom a slurry mixture, the mixtures being adjusted and maintained so asto be within the desired metal oxide stability area.

“Precipitated metal oxides,” as used herein, refers to metal oxidesformed or newly formed by precipitation from a mixture of a heated metalsalt solution and a heated aqueous oxidizing solution or a mixtureformed by addition of a metal salt to a heated aqueous oxidizingsolution, the mixtures being adjusted and maintained so as to be withinthe desired metal oxide stability area.

“Metal containing solution,” as used herein, refers to a metalcontaining solution selected from the group consisting of a slurry ofvirgin metal oxides, a regeneration slurry containing rinsed reactedmetal oxides, a slurry of loaded metal oxides, and a metal salt solutioncontaining disassociated metal cations. Metal containing solutions maycontain one or more metal oxides and/or one or more disassociated metalsalts.

“Manganese containing solution,” as used herein, refers to a metalcontaining solution where the metal is manganese.

“Aqueous oxidizing solutions” as used herein refers to an aqueoussolution containing an oxidant or oxidizer. The aqueous oxidizingsolution may contain a premixed solution containing both oxidant andbase.

“Primary metal,” as used herein, refers to a metal being processed toform a metal oxide, a primary metal oxide, incorporating one or moreforeign cations.

“Secondary metal,” as used herein, refers to a metal processed with aprimary metal but outside of the metal oxide stability area for thesecondary metal so as to provide foreign metal cations.

“Combined mixed process solution” as used herein, refers to a mixture ofa metal containing solution and an aqueous oxidizing solution which mayfurther contain foreign cations.

“Target pollutant,” as used herein, refers to the pollutant orpollutants that are to be captured and removed from a gas or aqueousstream. Examples of gas borne target pollutants that may be removed witha metal oxide sorbent include, but are not limited to, oxides ofnitrogen (NO_(X)), oxides of sulfur (SO_(X)), mercury (elemental,oxidized and particulate forms), mercury compounds, H₂S, totally reducedsulfides (TRS), mercaptans, chlorides, such as hydrochloric acid (HCl),carbon monoxide (CO), volatile organic compounds (VOC), and other heavymetals present in utility and other industrial process and waste gasstreams. Examples of aqueous borne pollutants that may be removed with ametal oxide sorbent include, but are not limited to, arsenic (As⁺³ andAs⁺⁵), lead mercury, and chromium.

“Reacted” or “loaded,” as used interchangeably herein, refers inconjunction with “oxides of manganese,” “metal oxides,” and/or “sorbent”to oxides of manganese, other metal oxides, or sorbent that hasinteracted with one or more target pollutants in a gaseous or aqueousstream whether by chemical reaction, adsorption or absorption. The termdoes not mean that all reactive or active sites of the sorbent have beenutilized, as all such sites may not actually be utilized.

“Unreacted” or “virgin,” as used interchangeably herein, refers inconjunction with “oxides of manganese,” “metal oxides,” and/or “sorbent”to oxides of manganese, metal oxides, or sorbents that have notinteracted with target pollutants in a gaseous or aqueous stream.

“Nitrates of manganese,” as used herein, refers to and includes thevarious forms of manganese nitrate, regardless of chemical formula, thatmay be formed through the chemical reaction between NO_(X) and thesorbent and includes hydrated forms as well.

“Sulfates of manganese,” as used herein, refers to and includes thevarious forms of manganese sulfate, regardless of chemical formula thatmay be formed through the chemical reaction between SO_(X) and thesorbent and includes hydrated forms as well.

“Reaction product,” as used herein, refers to and include the productsformed during the interaction of a sorbent, e.g., oxides of manganese,other metal oxides, or combinations thereof, and a target pollutantwhether by chemical, catalytic, or other reaction mechanism.

Applicants have developed methods of producing newly precipitated metaloxides, of treating commercially available virgin metal oxides, and ofregenerating loaded metal oxides, or reacted metal oxides throughprocessing in a continuous flow reactor or a batch oxidation vessel thatresults in the production of metal oxides useful, amongst otherapplications, as sorbents for pollutant removal. Metal oxides soproduced may exhibit high or increased loading capacity and/or valencestates as compared to reacted and virgin metal oxides of various forms,including a variety of commercially available metal oxides. Applicantshave additionally developed a system and process for cyclically loadingwith target pollutants and regenerating metal oxide sorbents, such asmanganese oxide or metal oxide compounds, utilizing batch processing ora continuous flow reactor that results in the production of usefulbyproducts.

Applicants have further found that metal oxides can be precipitated withcontrolled introduction of one or more foreign cations, e.g., K⁺, Na⁺,into their crystalline structure to desirably impact one or more of thephysical or reactive properties or characteristics of the metal oxidesand sorbents produced according to various embodiments of the methods ofthe invention. Controlled co-precipitation of two or more species ofmetal oxides (e.g., iron oxide and manganese oxide) as a metal oxidecompound can also be achieved, with or without incorporated foreigncations. Further still, Applicants have found that the precipitationmethods of various embodiments of the invention can be utilized to coata variety of different substrates of varying sizes, shapes anddimensions. Such substrates may be either reactive or inert and mayinclude, by non-limiting example, substrates such as metal oxideparticles, activated carbon particles, metal filtration media, polymericor other non-metallic filtration media to name a few. The metal oxidesof these precipitated coating may also incorporate foreign cations ormay be co-precipitated metal oxides. Precipitation onto substratesprovides sorbents or articles useful for numerous applications,including pollutant removal applications.

In various embodiments, the methods of the invention as disclosed hereinmay be utilized to process a variety of metal oxides. Metal oxide thatmay be processed in the methods and systems of the invention include,but are not limited to, those of metals known representative andtransition metals, such as iron, titanium, barium, lithium, magnesium,sodium, potassium and aluminum, to name a few. Further, rare earthmetals, alkali metals, noble metals and semi-conductive metals may alsobe processed in the methods and systems of the invention. Theaforementioned metals may be utilized to form metal oxides,co-precipitated metal oxides or to provide foreign metal cations to beincorporated into metal oxides. Metals of general interest are thosewith cations from which metal oxides can be precipitated to form metaloxides or that provide foreign metal cations that enhance the removalability of a first or primary metal oxide or that themselves form stablemetal oxides alone or in a metal oxide compound. For some applications,it is particularly beneficial if the meta oxide is one that will formeither soluble or thermally decomposable metal salts when reacted withtarget pollutants in a gas stream. Metal oxides that can yield reactionsproducts with these desired properties include, but are not limited to,both representative metals and transition metals. Of, the transitionmetals those from the fourth period of the periodic table areparticularly well suited. Generally, suitable metal oxides include, butare not limited to, oxides of any one of the following metals:magnesium, calcium, scandium, chromium, manganese, iron, nickel, copper,zinc, aluminum, yttrium, rhodium, palladium, silver, cadmium andcombinations thereof. These and other metals may form high valence metaloxides themselves or be integrated into the lattice structure of aprimary metal oxide through controlled addition during embodiments ofmethods of the invention. If the metal cations are not oxidized to ahigh valence state in the process, they may still be useful as foreignmetals in a hydroxide or lower valence metal oxide form. Other metalsthat may be useful in some form as a foreign metal include but are notlimited to cobalt, platinum, molybdenum, vanadium, and nickel.

Embodiments of Applicants' invention may be employed to convert metalcontaining solutions to high purity metal oxides with high valencevalues, strong affinity for target pollutants, and other desirablecharacteristics by controlling the reactions with attention to a metaloxide stability area. The metal oxide stability area refers to theregion or domain delineated by Eh and pH values for aqueous solutions atspecified temperatures, pressures and molarities in an electrochemicalstability diagram, such as presented by Pourbaix diagrams and theirequivalents, such as the Latimer Diagram or the Frost Diagram. Byunderstanding the metal oxide stability area and maintaining solutionconditions so that the solution conditions spend little to no time inregions of the Pourbaix diagram where undesirable side products arestable or can be formed, Applicants can predictably create or engineermetal oxides with superior characteristics, such as target pollutantcapture capability or loading capacity, as described throughout thisspecification.

Metal oxides produced by the methods and systems of the invention areuseful for various applications including removing pollutants fromgaseous streams. Applicants have developed systems and methods toexploit this attribute for, among other applications, pollutant removalfrom industrial gas streams. For example, Applicants have developed thePahlman Process™ Technology that removes NO_(X) and SO₂, among otherpollutants, from flue gases of industrial furnaces, boilers forelectrical generators, and other similar air emission sources.Applicants have also applied the ability of these metal oxides to removepollutants from gaseous streams to create superior sorbents forfiltration media used in personal respirators.

Metal oxides produced by the various embodiments of the invention arealso useful in aqueous pollutant removal. The metal oxides caneffectively remove difficult to capture pollutants and possess highloading capacity. Pollutants such as arsenic, present in water asarsenite (As⁺³) and arsenate (As⁺⁵) among other forms, hardness such ascalcium compounds and magnesium compounds, and other metallic andnon-metallic aqueous borne pollutants can be removed by embodiments ofthe invention with high capture rates and long sorbent or filter medialife.

Methods of Applicants' invention may be carried out in batch reactorsystems or a continuous flow reactor system. Without being bound bytheory, Applicants believe that the processing of loaded and virginmetal oxides and the precipitation of newly formed metal oxidesaccording to the invention in a heated aqueous solution system within acontinuous flow reactor system, as well as a batch reactor system,maintained within the desired metal oxide stability area maybeneficially affect a number of characteristics of the metal oxides.Such characteristics include, but are not limited to, one or more ofparticle size and shape, crystalline structure or morphology, porevolume, porosity, composition, surface area (BET), bulk density,electrochemical or oxidation potential, single and/or multiple foreigncations concentration, pollutant loading or removal capacity, andvalence states.

Batch reactor system embodiments of the invention involve mixing heatedoxidizing solutions having the desired pH-Eh-temperature combination atatmospheric pressure, with a source of metal ions to produce the desiredmetal oxides. This mixing may take place in a continuously stirredreactor vessel or some other batch reactor and the pH, Eh, and solutiontemperature, may be monitored and adjusted to ensure that solutionconditions remain favorable for the production of the desired metaloxides and solution conditions are rarely if ever favorable for theproduction of undesirable side products. Embodiments of Applicants'invention may be carried out using continuous flow reactors, whichallows for processing at elevated temperatures and at pressures aboveatmospheric. In either batch or continuous flow reactor systems,molarity may also be monitored and adjusted in methods.

Methods of the invention in various embodiments entail mixing orcontacting a metal containing solution with an aqueous oxidizingsolution, the aqueous oxidizing solution initially being prepared tohave Eh and pH values within a polyatomic ion, metal ion,co-precipitation, or a metal oxide stability area or to move solutionconditions initially into the polyatomic ion, metal ion,co-precipitation or a metal oxide stability area when contacted with themetal containing solution at process temperatures and pressures. Oncereaction begins, the solution parameters are monitored, and adjusted tomove and/or to maintain conditions within the metal oxide stability areaor co-precipitation stability area. The metal containing solution may bethe filtrate from rinsing of metal salt reaction products from reactedsorbent or may be prepared by dissolving metal salts in aqueoussolutions. Solution containing metal cations may also be prepared byleaching of metal values from metal containing materials, e.g.,commercially available metal oxides, crushed metal ore, or in situ orebodies with leach mining. Some metal oxides occur naturally in aninsoluble oxide form which must first be reduced through the use of areducing agent, and reacted with an anion to form a soluble metal saltor to provide disassociated metal cations in solution.

The aqueous oxidizing solution must be able to provide the requiredelectrochemical (oxidizing) potential (Eh) at the specified temperature,pressure and molarity and within the specified pH ranges to provide anEh-pH combination to achieve stable aqueous solution system equilibriumwithin the selected stability area, e.g., with manganese as the metal,permanganate, manganese ion, co-precipitation or MnO₂ stability area.Suitable oxidizers to name a few include, but are not limited to,persulfates, such as potassium peroxidisulfate (K₂S₂O₈), sodiumperoxidisulfate (Na₂S₂O₈), and ammonium peroxidisulfate ((NH₄)₂S₂O₈,chlorates, such as sodium chlorate (NaClO₃), perchlorates such as sodiumperchlorate (NaClO₄), permanganates, such as potassium permanganate(KMnO₄), oxygen (O₂) or air, ozone (O₃), peroxides, such as H₂O₂,organic oxidizers, such as peroxyacetic acid (C₂H₄O₃), andhypochlorites, such as sodium hypochlorite (NaOCl). Other oxidizerssuitable for use in the methods of the invention will be apparent tothose skilled in the art; it being understood that the electrochemicalpotential (Eh) of the preheated aqueous oxidizing solution, andtherefore the effectiveness of the methods of the invention, depends, inpart, upon the strength of the oxidizer and/or the concentration of theoxidizer in the solution. The oxidant may also be purchased commerciallyor produced in and fed from an electrolytic cell.

The pH of the solutions of the various embodiments of the invention ismonitored and is adjusted through the controlled addition of acids andbases. Examples of useful bases include but are not limited to alkali orammonium hydroxides, potassium hydroxides, and sodium hydroxides.Examples of useful acids include but are not limited to sulfuric,nitric, hydrochloric and perchloric acid to name a few. Applicants havefound it useful to match the cations of the oxidant and base. Forexample, where the oxidant is a persulfate, such as potassiumperoxidisulfate (K₂S₂O₈), the pH could be adjusted with a compatible orsuitable base, such as potassium hydroxide (KOH). If sodiumperoxidisulfate is used (Na₂S₂O₈), a compatible base would be sodiumhydroxide (NaOH); and with ammonium peroxidisulfate ((NH₄)₂S₂O₈),ammonium hydroxide ((NH₄OH) would be a compatible base. The acids orbases and other process additives are generally commercially availableand those skilled in the art would be able to readily identifycompatible process additives useful within the scope of the invention.

In the methods and systems disclosed herein, the conditions orparameters of aqueous systems are maintained within a metal oxidestability area or co-precipitation stability area, and sometimesstarting initially within a metal ion or polyatomic ion stability area.This is done with regard to electrochemical (oxidizing) potential (Eh)range and pH range at the prescribed system temperature at ambient orelevated atmospheric conditions (pressure) in order to provide an Eh-pHcombination to achieve stable solution equilibrium, as defined by the,metal oxide stability area or co-precipitation stability area asdelineated in, for example a Pourbaix Window diagram.

Applicants have found that metal oxides can also be processed using themethods of the invention by first preparing an aqueous oxidizingsolution with Eh and pH values that are either in the polyatomic ion,metal ion, or co-precipitation stability area or that moves the solutioninitially into the polyatomic ion, metal ion, or co-precipitationstability area when contacted with a metal containing solution underprocess temperatures and pressures.

With reference to FIG. 12, this can be more easily understood by usingmanganese as a specific example. A characteristic of most oxides ofmanganese species is non-stoichiometry; that is, most oxides ofmanganese molecules or MnO₂ species typically contain on average lessthan the theoretical number of 2 oxygen atoms, with numbers moretypically ranging between 1.5 to 2.0. The non-stoichiometrycharacteristic is thought to result from solid-solution mixtures of twoor more oxide species, and exists in all but the beta (β), orpyrolusite, form of manganese dioxide. Oxides of manganese having theformula MnO_(X) where X is about 1.5 to about 2.0 are particularlysuitable for dry removal of target pollutants from gas streams. However,the most active types of oxides of manganese for use as a sorbent fortarget pollutant removal usually have the formula MnO_(1.7 to 1.95),which translates into manganese valence states of +3.4 to +3.9, asopposed to the theoretical +4.0 state. It is unusual for average valencestates above about 3.9 to exist in most forms of oxides of manganese.Oxides of manganese may also include bound waters of hydration or watersof crystallization that create various hydrated forms of oxides ofmanganese molecules. Oxides of manganese processed by the invention mayinclude co-precipitated other metal oxides or foreign cations,represented by the formula yMnO_(X)2H₂O where y is a foreign cation. Theformula MnO₂, as used herein, symbolically represents all varieties ofmanganese dioxide including those with valence states ranging from +3 to+4, or MnO_(1.5-2.0), coprecipitated oxides of manganese, oxides ofmanganese with foreign cations, and oxides of manganese including boundwater. All chemical formulas used throughout are to be interpreted witha similar breadth of definition of species, and where chemical formulasare used as they are to be considered as encompassing the various formsof the compounds described and not to be limited to the single specieswith the exact stoichiometric composition of the chemical formula.

Referring now to FIG. 12, if the solution conditions are initially inthe polyatomic ion stability area for permanganate (MnO₄), after mixingof the two solutions, the pH of combined mixed process solution may, forexample, be allowed to drop from alkaline down into the acidic range,moving the solution into the MnO₂ stability area from the permanganatestability area. If the solution conditions are initially in themanganese ion (metal ion) stability area, after mixing of the twosolutions, the pH of the combined mixed process solution may be allowedto rise from the acidic into the alkaline range and, as long as Eh ofthe solution is maintained at a high enough value to prevent formationof lower valence metal oxides, the solution will move into the MnO₂stability area from the manganese ion stability area. These techniquescan be employed in the various embodiments of the invention to produceprocessed metal oxides of desired oxidation state and to avoid formationof lower metal oxides, such as Mn₂O₃ and Mn₃O₄. This increases the“yield purity” making the metal oxides useful, amongst otherapplications, as a sorbent for removing target pollutants from gas oraqueous streams. Further, this technique serves to minimize the oxidantutilization thus providing cost savings.

In this example, the polyatomic ion or permanganate stability area ofthe Pourbaix diagram of FIG. 12 is above that of the MnO₂ stability areaand has a higher Eh level for a given pH level. The manganese ionstability area is below that of the MnO₂ stability area and has a lowerEh level. If solution conditions begin in the permanganate stabilityarea, the process solution will develop the purple permanganate colorand when, during the process, the pH drops moving the solution to enterinto the MnO₂ stability window, will start precipitating MnO₂ sorbent.Whether solution conditions begin in the polyatomic ion stability areaor the metal ion stability area, keeping solution conditions out ofregions of the Pourbaix diagram associated with undesirable sideproducts is highly beneficial in precipitation methods as this avoidsformation of lower valence state metal oxides that have to be oxidizedup to the desired oxidation state metal oxides which would result indepletion and consumption of oxidant; and therefore, less oxidant can beused. Therefore, Applicants have found that the batch oxidation andcontinuous flow reactor needs to be equipped with the appropriatesystems and controls for rapid and adaptive controlling of the streamprocess conditions. This process can be used to pretreat virgin sorbentand to regenerate reacted sorbent and yields processed oxides ofmanganese with increased loading capacity and/or oxidation strength.

This same technique can be utilized with other metal oxides, e.g., ironoxide. Referring to FIG. 13, the polyatomic ion stability area for FeO₄⁻² and the metal ion stability area for Fe⁺² are shown bordering theFe₂O₃ area. The preceding discussion relative utilizing this techniquewhere manganese is the metal is equally applicable to iron and othermetals.

Although the following discussion focuses on principles applicable tothe MnO₂ stability area, these principles will be understood by thoseskilled in the art to also be generally applicable to other metal oxidestability areas. The MnO₂ stability area for an aqueous system variesbased upon the conditions of the system and may shift or drift asreactions in the aqueous system proceed. For example, changes indissolved manganese ion concentration, oxidizer concentration, pH, Eh,solution temperature and pressure, and various dissolved ions may affectthe boundaries of the domain or region of stability for MnO₂. Theaqueous oxidizing solution within the reactor system of the inventionare typically at temperatures near, at, or greater than boiling or 100°C. at atmospheric pressures and at pressures at or greater thanatmospheric. The effects of such changes or different conditions uponthe boundaries of the MnO₂ stability area on a Pourbaix Eh-pH diagramcan be determined either by empirical data derived from experimentationor generated from theoretical calculations which can be carried outmanually or with computer software programs known to those skilled inthe art, such as HSC Chemistry distributed by Outokumpu Oy of Finland orOLI Systems, Inc. of New Jersey, USA. Software may also be written todetermine the MnO₂ stability area as defined by other diagrams, such asthe Latimer Diagram or the Frost Diagram.

With reference to FIGS. 11 and 12, the impact of system conditions onthe MnO₂ stability area is illustrated with respect to Pourbaix Diagramsfor aqueous systems at 25° C. and at ambient pressure at sea level. InFIG. 11, the ranges of pH and Eh values for thermodynamically stableaqueous solution systems of various manganese compounds are illustratedin graph form for aqueous solution systems at 25° C. and a 1 mole/litermanganese ion concentration. FIG. 12 similarly illustrates ranges of pHand Eh values for an aqueous solution system at 25° C. but at a 1.0×10⁻⁶mole/liter manganese ion concentration and ambient pressure at sealevel. The Pourbaix Diagrams depicted in FIGS. 11 and 12 were derivedfrom the diagram presented in Atlas of Electrochemical Equilibria inAqueous Solutions,” Marcel Pourbaix, pages 286-293, National Associationof Corrosion Engineers, Houston, Tex. A comparison of the boundaries ofthe two shaded areas on FIGS. 11 and 12 is illustrative of the differentstability areas that exist under different system conditions. ThePourbaix Diagrams of FIGS. 11 and 12 are provided by way ofillustration. It should be understood that such diagrams would representdifferent MnO₂ stability area regions at different temperatures,pressures and molarities and are not intended to represent a diagramreflecting process conditions within either a batch or continuous flowreactor operated in accordance with the methods of the invention. Infact, the methods of the invention can be carried out at ambienttemperatures and pressures as well as at elevated temperatures and atpressures above atmospheric.

In the methods and systems disclosed herein, the conditions orparameters of aqueous solution systems within a reactor in accordancewith embodiments of the invention are monitored and maintained relativeto the metal oxide stability area (or co-precipitation or metal oxidestability area when other metals are processed) with regard toelectrochemical (oxidizing) potential (Eh) range and pH range at theprescribed system molarity, temperature and pressure in order to providean Eh-pH combination to achieve stable solution equilibrium, as definedby the metal oxide stability area as delineated in, for example aPourbaix Diagram, such as those depicted in FIGS. 11-17.

In an embodiment of methods of the invention, the constituents of theaqueous solution within the continuous flow reactor are the metalcontaining solutions, along with the oxidizer or oxidizers in theaqueous oxidizing solution and the base or acids that may be addedthereto which are mixed together to form a combined mixed processsolution. During processing, the mixed process solution within thecontinuous flow reactor system must be moved to and maintained at orwithin the boundary area delineated by the prescribed combination of Ehand pH ranges as the solution moves down the reactor. In order toaccomplish this, temperature, pressure, molarity, Eh, and/or pHadjustments must be made through the addition of oxidizer, base, acid ormanganese and other ions as the solution moves through the continuousflow reactor. To this end, Applicants typically utilize a preheatedaqueous oxidizing solution as described above containing an oxidizeralso referred to interchangeably herein as an oxidant.

The methods and systems of the invention, whether for regeneration,pretreatment or precipitation, may involve and employ Applicants'recognition that metal oxides, e.g., oxides of manganese, iron oxides,or the metal oxide, processed in an aqueous continuous flow reactorsystem in which conditions and parameters such as but not limited to:temperature, pressure, pH, Eh, molar concentration of the constituents(molarity), and retention times are initially prepared to be in thepolyatomic ion, metal ion, co-precipitation, or metal oxide stabilityarea and thereafter monitored, adjusted and maintained within the metaloxide stability area will yield metal oxides having high pollutantloading capacities and/or high oxidation states and/or other desirableproperties. In its various embodiments, the invention and the methodsand systems thereof provide for rapid, adaptive and stable processing ina continuous flow reactor of metal oxides as compared to the methods andsystems currently know in the art. Amongst other uses, metal oxides thusprocessed are suitable for use as a sorbent in dry and wet gaseouspollutant removal systems and are particularly suitable for use in drypollutant removal systems. They are also useful as sorbents in aqueousapplications, for example in the removal of Arsenic in water supplies inaddition to being utilized in batteries or a variety of commercial,industrial and other applications, unrelated to pollutant removal, thatincorporate or employ metal oxides.

Depending upon the conditions and constituents of the aqueous solutionwithin the continuous flow reactor system, the pH range of the boundarymay be acidic, near neutral, or basic. In short, processing may becarried out over the full pH spectrum. However, the oxidizer strength orconcentrations required at the extremes of the pH spectrum may make suchprocessing uneconomic though nonetheless achievable. As the reactionsproceed, metal oxides are being produced and the oxidizer is beingconsumed, the system may tend to shift away from the desired pH range,in which case the addition of a suitable base or acid will helpaccomplish the necessary adjustment to maintain the aqueous solutionwithin the continuous flow reactor system within the appropriate Eh-pHrange of the metal oxide stability area required to predominantlyproduce the desired metal oxide or metal oxide compound.

Continuous flow reactors are known in the art and may be provided invarious configurations and may be equipped with a number of componentsand utilized in the methods and systems of the invention. As shown inFIG. 1, a continuous flow reactor is show as a section of serpentinepipe and provided with an orifice 92, a static mixer 15 and abackpressure valve 94. It should be understood that the continuous flowreactors may be also be provided with a plurality of ports forintroduction or injection of solutions for making adjustments incombined mixed process solution conditions at different locations alongthe lengths of pipe forming the continuous flow reactors. For example, aport 96 is shown in FIGS. 1-5, as an oxidant/base/acid addition. Aplurality of ports 96 may be provided for addition of these and otherconstituents or for purging of process solutions from continuous flowreactors. Continuous flow reactors may be a single length of pipe,lengths of pipe with pipe “branches” or interconnected lengths of pipeequipped with diverter valves to direct the flow of process solutions.The branched pipe or interconnected lengths of pipe may be of differentlengths allowing for process solutions to be directed from a main pipelength to longer or short pipe lengths when system parameters indicatethat either longer or short processing residence times are required.Such configurations are one of several ways that residence time can beregulated or controlled in the systems and methods of the invention. Itshould therefore be understood that the continuous flow reactor depictedin the Figures is being provided solely for illustrative purposes.

Applicants have found it beneficial to maintain pH relatively constantduring processing. Alternatively, the introduction of additionaloxidizer to bring the system within the appropriate Eh range as pHdrifts or shifts in the aqueous system may also beneficially accomplishthe necessary adjustment. The aqueous solution within the continuousflow reactor system is, and therefore the methods and systems of theinvention are, dynamic and adaptive with necessary adjustments beingmade not only by introduction of acid or base but with introduction ofoxidizer along with changes in temperature, molarity, and pressurewithin the continuous flow reactor.

Although the following discussion focuses on an exemplary application ofembodiments of the invention directed toward the production of oxides ofmanganese and the MnO₂ stability area, these principles will beunderstood by those skilled in the art to also be generally applicableto production of other metal oxides (also referred to as “metal oxidecompounds”) with attention to their particular metal oxide stabilityareas or co-precipitated metal oxides with attention to theco-precipitation stability area, or precipitation onto a substrate. Aspreviously noted, oxidant may be provided in an aqueous oxidizingsolution containing only an oxidant with base being separately provided.However, Applicants have found it useful to utilize an aqueous oxidizingsolution created by premixing the oxidant and base solutions in specificquantities thereby creating a premixed solution of oxidant and baseoxidizing solution termed “premixed oxidant/base solution”. Thispremixed oxidant/base solution is prepared with the desired pH-Ehcombination and can be prepared, maintained, or adjusted by increasingor decreasing the amounts or molarity of oxidant, acid, base,constituent concentrations, temperature, and/or pressure adjustment, asappropriate, so that the conditions are adjusted to remain within theMnO₂ stability area when the aqueous oxidizing solution is contactedwith the manganese containing solution.

Through their understanding of the relationships between the systemparameters of the MnO₂ stability area and application thereof toconditions of a given aqueous system within a continuous flow reactor,Applicants are able to achieve stable and controlled regeneration,pretreatment, and precipitation so as to rapidly and adaptively yieldoxides of manganese having equal or increased loading capacity whencompared to the untreated commercially available EMD and CMD oxides ofmanganese (NMD, EMD, and CMD) or when compared to loaded oxides ofmanganese. At a given pH, Eh, temperature, pressure, and molar rangeswithin the MnO₂ stability area, the desired manganese valence state(theoretically close to +4) will exist. Thus, there is no propensity forMn compounds at or close to +4 valence state to degrade to +3 or +2valence states. However, if conditions are not maintained within theMnO₂ stability area such degradation may occur.

Applicants have found that oxides of manganese regenerated or pretreatedor precipitated (newly formed) within a continuous flow reactor from anaqueous oxidizing solution that is contacted or mixed with a manganesecontaining solution and subsequently that are maintained within the MnO₂stability area will exhibit a Mn valence state of close to +4 andexhibit target pollutant loading capacities equal to and/or greater than(increased) the loading capacities of virgin or loaded oxides ofmanganese.

Though preheating is a desirable and sometime required step, it may notbe required for aqueous solution systems processed in a continuous flowreactor according to the methods of the invention as long as the timerequired to bring the aqueous solutions up to their desired temperaturedoes not cause the formation of undesirable or untargeted constituents.With monitoring of Eh, pH, temperature, pressure, and molarconcentrations an operator can make necessary adjustments in order tomaintain or return the process solution conditions in a continuous flowreactor to within the MnO₂ stability area. Such monitoring and adjustingcan also be automated utilizing electronic probes or sensors andcontrollers as discussed later herein below.

In the various embodiments of the invention disclosed herein, thesystems in which the methods of the invention are carried out all havecommon or corresponding components that are substantially the same.Though referred to, in appropriate instances by slightly different terms(for purposes of clarity) and being identified with corresponding butdifferent reference numbers in the figures and the disclosure hereinbelow, their operation and function will also be understood to besubstantially the same and equivalent. To the extent that there areoperational or functional differences, they are identified and discussedas appropriate. Common system components include a continuous flowreactor in which regeneration, pretreatment and precipitation arecarried out; agitation devices such as static mixers and probes fortemperature, pressure, Eh, pH, and TDS (total dissolved solids)measurement with which the continuous flow reactor and other systemcomponents may be equipped. The continuous flow reactor is also equippedwith a heating unit, such as a heater or heat exchanger (not shown inthe figure hereof) for adding heat to and maintaining the temperature ofthe solutions in the vessels. In one such embodiment, a jet-cookerdesign which incorporates steam injection of the process streams, e.g.oxidant/base premix and metal containing stream can be employed andadditional process streams such as secondary metal containing solutionfor introduction of foreign cations may similarly be injected. Thoseskilled in the art of jet-cooker design and operation can configure thecontinuous flow reactor to use steam as a primary heat source and toprovide adequate mixing and contacting of the solutions at point ofcontact. Steam may not only be used for controlling molarities but alsoto control temperature in the continuous flow reactor. This is usefulbecause a separate heat exchanger does not have to be utilized andtemperature can also be controlled with a backpressure valve at the endof the continuous flow reactor.

When regenerating oxides of manganese with the methods of the invention,reacted sorbent is processed in a preheated premixed oxidant/baseaqueous solution within the continuous flow reactor under controlledconditions, specifically within the MnO₂ stability area, to produceregenerated oxides of manganese. The regeneration methods of theinvention can be understood with reference to FIGS. 1-3 which depictdifferent possible embodiments of a regeneration system 10 of theinvention in block flow.

Turning to FIG. 1, loaded oxides of manganese or loaded sorbent isrinsed or washed with an aqueous solution in the pre-oxidation sorbentrinse 12 of regeneration system 10 (without the precipitation subsystem30 shown in FIG. 3). The rinse step serves to wash away reactionproducts from the surface of reacted oxides of manganese sorbentparticles along with impurities and very fine particulate matter.Regeneration, however, may be conducted without the rinse step asdiscussed with reference to FIG. 2 herein below. Following rinsing, therinsed sorbent is separated from the rinse solution to provide rinsedsorbent or rinsed oxides of manganese or sorbent and a pre-oxidationfiltrate.

Filtration may be carried out using any of a variety of suitablefiltration techniques and devices known to those skilled in the art. Aseparate filtration device may be used following pre-oxidation rinse 12or the filtration device may be incorporated in and part ofpre-oxidation rinse 12. The filtrate will contain recoverable values,such as cations and anions from disassociated reaction products. Forexample, where the reaction products are manganese salts, such asmanganese sulfate (MnSO₄) and manganese nitrate (Mn(NO₃)₂), :Mn⁺², SO₄⁻², NO₃ ⁻¹, spectator ions, suspended solids or other particulates. Asdiscussed later herein below with reference to FIGS. 3, 5 and 6, thesevalues can be recovered from the pre-oxidation filtrate throughoxidation and precipitation of the Mn⁺² ion as a solid precipitatedoxides of manganese; and with further processing the sulfate or nitrateanions can be recovered and formed into useful and marketableby-products, e.g., fertilizers, chemicals or explosive products orrouted for disposal as required.

After rinsing and separation, an appropriate quantity of water is addedto the rinsed sorbent to create a rinsed sorbent slurry capable of beingpumped and introduced or conveyed to continuous flow reactor 14 which isequipped with at least agitation and mixing device 15, shown as staticmixer 15 in FIG. 1. Any of various static mixing or agitation devicesknown to those skilled in the art to be suitable for mixing solutions orsolid-liquid slurries so as to keep the solid oxides of manganeseparticles generally suspended in solution as they move down continuousflow reactor 14 can be utilized.

As illustrated in FIG. 1, the continuous flow reactor 14 is equippedwith temperature, probe 13A, pH probe 13B, Eh probe 13C and pressureprobe 13D. These probes are utilized to measure their respectiveparameters in the solutions or slurries processed in continuous flowreactor 14 and may be in electronic communication with a controller aslater discussed herein with reference to FIG. 8 and equally applicableto FIGS. 7 and 9.

Continuous flow reactor 14 is depicted in FIG. 1 with a single staticmixer 15 and a single orifice 92. It should be understood thatcontinuous flow reactors may be provided with a plurality (two or more)of agitation and mixing devices and orifices to assure proper andcontinuous mixing and/or to allow introduction of additional amounts ofpremixed oxidant/base solution and rinsed sorbent slurry as needed. Thepremixed oxidant/base solution and rinsed sorbent slurry may beseparately introduced or introduced after prior mixing of the two atdifferent points along the continuous flow reactor 14. The rinsedsorbent slurry is mixed with a preheated premixed oxidant/base aqueoussolution from oxidant/base premix vessel 11 to form a slurry, referredto herein as the regeneration slurry. The two process streams, therinsed sorbent slurry and the premixed oxidant/base solution, are bothmetered into the continuous flow reactor separately or as a regenerationslurry, and depending upon configuration or process design may firstenter through orifice 92. Orifice 92 provides a pressure drop in thesystem which aids in the creation of oxides of manganese particlecharacteristics useful in target pollutant capture. The resultingmixture or regeneration slurry is monitored and/or adjusted, asnecessary, by addition of oxidant, acid, or base concentrations, withtemperature, and/or pressure adjustment, as appropriate, so that theconditions are adjusted to remain within the MnO₂ stability area.

Prior to introduction into the continuous flow reactor, both thepremixed oxidant/base aqueous solution and the rinsed sorbent slurry maybe preheated. For example for some applications, the solution and slurrymay be preheated to temperatures above ambient. For other applicationsthey may be preheated to temperatures that are at least at or near 100°C. or to such higher temperature as appropriate as the oxidant cantolerate without significantly decomposing. Within the limits of oxidantdecomposition sensitivity, the aqueous oxidizing solution can bepreheated to temperatures approaching processing temperatures at givenoperating pressures within continuous flow reactor and as required to bewithin the MnO₂ stability area. In this and all other embodimentsutilizing a continuous flow reactor of the method according to theinvention, the two solutions can alternately be heated to temperaturesin excess of 100° C. before being brought into contact. However, certainoxidants used in the Applicants' invention tend to decompose attemperatures in excess of 100° C., thereby causing the undesirableoccurrence of oxidant decomposition prior to the sought after reactionwith manganese ions while other oxidants do not decompose atsubstantially elevated temperatures and may be heated to usefultemperatures in excess of 100° C. prior to mixing. The manganesecontaining solution, the rinsed sorbent slurry, and the aqueousoxidizing solution, the premixed oxidant/base solution may be introducedwithout heating and subsequently heated as they enter continuous flowreactor 14 by a heating unit incorporated into continuous flow reactor14. Further, for those oxidants sensitive to elevated temperatures, oncethe aqueous oxidizing solution contacts and is mixed with the manganesecontaining solution to form the combined mixed process solution,reactions in the continuous flow reactor have begun, temperatures can beelevated above the temperature at which the oxidant would decompose asthis may then facilitate or accelerate process chemistry.

Just as temperatures may be elevated within the continuous flow reactorsin the methods of the invention, pressures may also be elevated aboveatmospheric conditions. Backpressure valves may be incorporated at theend of the continuous flow reactor. This valve serves several functions.The valve may be adjusted manually or automatically. External controlsmay also be incorporated to adjust the valve automatically to a pre-setset point. By moving the valve to a more closed position the pressuremay be increased and likewise by opening the valve within the continuousflow reactor the pressure decreased. These positions also have an effecton temperature within the continuous flow reactor. A more closed valveposition will increase temperature and a more open valve position willdecrease temperature. The position of the valve works in conjunctionwith an external heating apparatus to control temperature and pressurewithin the continuous flow reactor. Valve design may include but is notlimited to diaphragm, ball, or slide valves. The use of back pressurevalves for regulating and controlling system pressures is known to thoseskilled in the art. Their use and adaptability for application in acontinuous flow reactor would be readily understood by the skilledartisan as well as use of a controller to make pressure adjustments.

Regeneration of the rinsed slurry may be carried out at various processtemperatures as required in order to maintain the aqueous solutionsystem with the MnO₂ stability area as other system parameters shiftduring processing. Applicants have found that processing temperatures inexcess of 100° C. may be utilized in processing oxides of manganesesorbent within the continuous flow reactor, as long as solutions andslurries are maintained within the MnO₂, or appropriate metal stabilitywindow. There may be heating units, such as heat exchangers or otherdevises known to those skilled in the art of heating solutions, atdifferent points along various lengths of a continuous flow reactor.

Determining which parameter adjustments to make is a matter ofengineering or operator choice as long as the adjustment moves systemconditions into or maintains them within the MnO₂ stability area withmanganese as the metal or within the appropriate stability area forother metal oxides or co-precipitated metal oxides.

The preheated aqueous premixed oxidizing/base solution provides therequired electrochemical (oxidizing) potential (Eh), within thespecified temperature, pressure, and pH range to yield regeneratedoxides of manganese having high loading capacities and/or highoxidations states. Through use of static mixers, the regeneration slurryin continuous flow reactor 14 is continuously mixed and the pH of theslurry is adjusted by appropriate means, e.g., addition of acid or base.

The regeneration slurry of oxides of manganese are allowed to remainwithin the continuous flow reactor for a time sufficient to achieve anincreased oxidation state and/or a target pollution loading capacityequal or greater than that of virgin oxides of manganese sorbentoriginally utilized to capture target pollutants. Applicants have foundthat oxidation strength and/or load capacity of the MnO₂ tends toincrease with an optimum retention time determined for a specifictemperature, pressure, pH, Eh, and molar concentrations, as does theproduction of MnO₂. With sufficient retention time substantially all ofthe oxides of manganese contained in the regeneration slurry will beregenerated, until the aqueous solution will contain substantially onlyMnO₂ and useful by-products, such as potassium or sodium nitrates orsulfates for example, left in solution before exiting the continuousflow reactor.

Retention times can be increased to the desired duration by adding to orrouting the combined mixed process solution through additional pipelengths of a continuous flow reactor, changing the pipe diameter,slowing down the injection rate of the solutions, changingconcentrations of process solution constituents or by other means knownto those skilled in the art of continuous flow reactor design andoperation. If monitoring indicates that processing is complete, thecombined mixed process solution can be purged from continuous flowreactor 14. Continuous flow reactors may be provided with multipleflushing ports, (not shown) for this purpose or to vacate the processsolution for any reason or for general routine maintenance and cleaningof a section of pipe forming a continuous flow reactor.

Retention times may also be regulated or controlled by changing inputmolarities or concentrations of chemical constituents. Adjusting theamounts of manganese or other metal, whether in a slurry ordisassociated ions in solution, or the amounts of oxidant can varyrequired processing time and thus retention time. For example, if themanganese containing solution has high concentrations of manganesevalues, the amount of oxidant may be increased thereby reducing theretention time required to for the desired end product. Similarly, if aslower processing time is desired (increased retention time) the amountof oxidant may be decreased, but preferably not below a concentrationneeded to complete processing of manganese values to MnO₂.

Applicants have found that with an optimal regeneration slurry retentiontime the portions of the solid rinsed oxides of manganese particles thathave had their reactivity or target pollutant loading capacity reduced,through lowering of valance state, are oxidized up to valance statesclose to +4.

At the end of the continuous flow reactor is a backpressure valve 94 orother device known in the art, which controls the pressure within thecontinuous flow reactor. Just as temperatures may be elevated within acontinuous flow reactor, pressure may also be elevated in excess ofatmospheric pressure, monitored, regulated and controlled to desiredprocessing pressures and adjusted according to process dynamics. Valve94 in conjunction with heating units allows the temperature and pressureto be raised and maintained within the pipe to the appropriateprocessing temperature and pressure as defined by the MnO₂, or asappropriate, other stability area. The regeneration slurry exitingbackpressure valve 94 or similar device or from flushing points isrouted to a wash and rinse process where the MnO₂ sorbent is separatedand filtered from the solution leaving a filtrate and regenerated oxidesof manganese filter cake. Filtration can be preformed by techniquesknown to one skilled in the art of filtration, such as but not limitedto hydroclones, drum filter, moving bed filter, or a filter press.

Separation of the regenerated oxides of manganese and the oxidationfiltrate may be performed at a minimal temperature preferably close toabout 100° C., and more preferably close to the operating temperature incontinuous flow reactor 14. This separation may less preferably beperformed at temperatures below the minimal temperature. Allowing thesolution containing regenerated oxides of manganese and the aqueousoxidizing solution to cool to temperatures below the solubilitytemperatures for residual or spectator ions in solution, for example,but not limited to K⁺¹ and SO₄ ² can result in the precipitation ofsolid salts such as K₂SO₄. So as a practical matter, temperatures abovethe solubility temperature of residual ions may be the minimal desirabletemperature. Through experimentation, it has been recorded that allowingsalts at certain levels to precipitate with the regenerated oxides ofmanganese sorbent lowers the target removal efficiency and loading ratesand should therefore be avoided. The separated regenerated sorbent orregenerated oxides of manganese or other metal oxides are then furtherrinsed with water to wash away any remaining spectator ions.

In FIG. 1, this is illustrated as two separate steps: 1) filtering andseparating the regenerated oxides of manganese from the regenerationslurry in filtration unit 16 to provide an oxidation filtrate; and 2)rinsing the separated, regenerated sorbent with water to wash awayremaining spectator ions in the regeneration rinse 17.

Any of a variety of suitable filtration techniques and devices known tothose skilled in the art may be utilized for this purpose. It should benoted that the filtration and rinsing step could be carried out incombined filtration and rinsing equipment known to those skilled in theart. Further, as with the pre-oxidation rinse, the filtration unit 16may alternatively be incorporated into and as an integral part ofcontinuous flow reactor 14. The rinsing of the metal oxides leaving thecontinuous flow reactor should be of sufficient duration and withsufficient volume of water as to remove disassociated ions associatedwith the oxidizer, base, and acid in the aqueous oxidizing solution to asuitable level. The presence of these ions in the regenerated sorbent inexcessive amounts may negatively impact the loading capacity or removalefficiency of the regenerated oxides of manganese. This is not to saythat regenerated oxides of manganese that are not so rinsed will beineffective for removal of target pollutants because in fact they may beso utilized without the rinse or with less than thorough rinsing andgood removal rates can be achieved. However, the regenerated oxides ofmanganese may be more efficiently utilized following rinsing. This isequally applicable to oxides of manganese pretreated or precipitatedaccording to the methods of the invention.

Various measurement techniques and devices known to those skilled in theart can be employed to determine the level or concentration of such ionsin rinse water and thereby determine whether the oxides of manganesehave been adequately rinsed. Such techniques include measurement ofconductivity, resistivity, total dissolved solids (TDS) or otherindicators of the level of disassociated ions and/or dissolved solidsand fine particulates in a solution, such as specific gravity or densityor chemical analysis. By way of example and not limitation, TDSmeasurements of the oxidation filtrate taken by Applicants have been inthe range of 80,000-200,000 ppm, representing the disassociated ionsfrom the oxidant, base or acid and other possible dissolved solids orfine particulates associated with the regeneration. The rinse stepshould generally being designed to remove such ions, solids andparticulates from the regenerated oxides of manganese to an acceptablelevel or tolerance. Where precision is required the vessel or apparatusin which the rinse and/or filtration is carried out should be equippedwith an appropriate probe for monitoring or measuring conductivity,resistivity, TDS level or other indicator of the mount of dissolvedsolids and particulates in solution which may generally be referred toas a TDS probe and coupled with or part of a TDS controller or TDScontrol element. The TDS controller in response to an input from the TDSprobe can regulate or control the level or duration of the rinse and/orfiltration step by signaling the termination of the rinse and/orfiltration step once the desired TDS set point has been reached.

Continuous flow reactors may also optionally be provided with TDS probesin electronic communication with controller 67 (FIG. 8) or a TDScontroller. TDS levels are an indicator of the concentration ofmanganese and other ions in the process solution in the continuous flowreactor. TDS level data allows a controller, such as controller 67, tocalculate manganese ion molarity and determine the required Eh and pH atprocess temperatures and pressures required to precipitate oxide ofmanganese. Phrased alternatively, TDS level data can help determine theMnO₂ stability area for given conditions in the process solution in acontinuous flow reactor or the required Eh and pH level of the aqueousoxidizing solution to be mixed with a manganese containing solution.

With monitoring of such measurements, the rinse step can be carried outuntil the oxidation filtrate reaches the desired level based upon themeasurement technique employed. Through a series of regeneration cyclesand loading cycles, the acceptable level or tolerance for the given useto which the regenerated oxide will be put can be determined, as well asthe volume, flow rate and duration of the rinse in order to establish orstandardize operating procedures. Although lowering the TDS of thefiltrate generally favorably impacts target pollutant removal efficiencyand loading rates, Applicants have found that oxides of manganeseprepared according to the methods of the invention may be utilized fortarget pollutant removal with or without the rinsing step. Applicantshave achieved adequate target pollutant removal with regenerated oxidesof manganese that is not rinsed prior to use as a sorbent, but have seenbetter removal at measured TDS levels in the filtrate of less than100,000 and even better performance at less than 10,000.

In some of the various embodiments of methods according to theinvention, invention, metal oxide sorbent exits either the continuousflow reactor or the batch process and is directed to a metal oxide rinse17. During this stage of the process, the processed metal oxides orsorbent can be rinsed to a specified level of total dissolved solids(TDS), as measured in the metal oxide filtrate. As earlier mentioned, ithas been found that the level to which the sorbent is rinsed affects theremoval capabilities of the sorbent produced. For example, NO_(x)removal and utilization of the sorbent appears to improve with sorbentthat has been rinsed to a lower TDS value, below about 10,000 ppm ormore preferable below about 5,000 ppm. Whereas for SO_(x) higher removaland utilizations were achieved with sorbent that had not been rinsed tolow TDS values, ranging between about 10,000 ppm to about 30,000 ppm. Asnoted, sorbent or metal oxides may be processed with higher or lower TDSrinse values; however, at higher levels sorbent utilization and/orremoval efficiencies may diminish for some applications. During targetpollutant capture where the target pollutant is SO_(x), the sulfatespecies bound to the manganese oxide sorbent as manganese sulfate canact as a catalyst for additional target pollutants and can assist inremoving higher quantities of target pollutants, thus increasing sorbentutilization. For example, the manganese sulfate reaction products boundon the surface of the manganese dioxide sorbent during pollutant removalhave been seen to act as a catalyst for certain species of mercury (Hg)present in some industrial flue gas streams. With sorbents preparedaccording to the disclosed methods, Applicants' conducted testsutilizing a Pahlman Process™ pollutant removal system showing that afterthe sorbent had reached its capacity for NOx and SOx capture, thepartially loaded sorbent still oxidized 100% of elemental mercury (Hg⁰)to its oxidized form oxidized mercury (Hg⁺²). The sulfates were servingas a catalyst in the reaction converting elemental mercury)(Hg⁰) tooxidized mercury (Hg²⁺). Therefore, regulating the TDS level in theeffluent stream directly controls the concentration of sulfatescontained with the sorbent, which could allow the operator to manipulateutilization and reactions occurring during pollutant capture.

Returning to FIG. 1, the wet regenerated oxides of manganese, if beingutilized in a dry target pollutant removal system such as of the PahlmanProcess™ Technology, is first routed for drying to a dryer 18, referredto as sorbent dryer 18 in the figure. Oxides of manganese may beintroduced into pollution removal systems as a dry powder, a wet filtercake, or slurry by a slurry or spray feeder. There are current spraydrying applications, such in the dry lime absorbers that utilize thisinduct drying technology and those familiar with the art of spray dryingwould be familiar with the technology. In dry removal systems, the wetfilter cake and sprayed slurry may be “flash dried” upon contact withindustrial gas streams which may be introduced at elevated temperaturesinto the pollutant removal systems. For such other applications thedrying step may not be necessary and the wet or moist filter cake may beconveyed to a filter cake feeder. Similarly, with injection, slurry,spray or spray injection feeders, once adequately rinsed, theregenerated oxides of manganese need not be further filtered orseparated. With addition of such amount of water as necessary, a sorbentslurry may be formed. The sorbent can then be conveyed to the slurryfeeder. In duct drying, spray drying or flash drying can also have theaffect of increasing the sorbents utilization. In the spray dryingprocess, water soluble target pollutants can get dissolved in thesurface water and as the surface water evaporates, leaving the targetpollutant in contact with the sorbent, thereby positively affectingtarget pollutant capture. Once again, the benefits of spray drying orflash drying that are known to those skilled in the art, apply to theapplicants' invention as well.

However, when the oxide of manganese sorbent is to be introduced as adry particulate or powder, both drying and comminuting to size theoxides of manganese particles is typically performed. Dryer 18 may be akiln or other suitable dryer used for such purposes and known to thoseskilled in the art. Dryer 18 may utilize waste heat generated bycombustion which is transferred or exchanged from combustion or processgases at an industrial or utility plant. When drying is required thetemperature should be below the thermal decomposition temperature ofoxides of manganese but sufficiently high so as to drive off surfacewater or moisture without removing any waters of hydration or waters ofcrystallization. Temperatures around 100° C. to 160° C. have been foundto be adequate for this purpose. Drying can be conducted at lowertemperatures but drying time may be uneconomically extended; and athigher temperatures, which can be utilized in Applicants' invention,short drying time will have to be closely observed so as to avoidthermal decomposition of the oxides of manganese, driving off structuralwater, or undesired damage to the crystalline structure of the oxides ofmanganese.

In another embodiment of the regeneration methods of the invention,loaded sorbent is processed without a pre-oxidation rinse. This isillustrated in FIG. 2, where the loaded sorbent first is mixed with anadequate quantity of water to form a loaded sorbent slurry and metered,through appropriate means known to those skilled in the art, directlyinto orifice 92 leading into continuous flow reactor 14, referred toherein as continuous flow regeneration/precipitation reactor 14, ofregeneration system 10 without a pre-oxidation rinse. The system 10, asdepicted, includes at least one static mixer 15, probes 13A-13D,filtration unit 16, rinse 17, dryer 18, and comminuting device 19. Inthe interest of avoiding undue repetition, Applicants note that thecomponents of system 10 in FIG. 2, absent the pre-oxidation rinse 12,are essentially the same components as that of system 10 in FIG. 1 andthat the function and operation of the corresponding system componentswill be the same in both embodiments of the systems and of the methodsof the invention as depicted in FIGS. 1 and 2. The statements made aboveregarding the corresponding counterpart components and process steps inregeneration system 10 of FIG. 1 and operating conditions and parameters(temperature, pressure, Eh, and pH) are equally applicable to thecomponents of system 10 of FIG. 2 and therefore they are not repeatedhere. Further, in this embodiment, the method proceeds in substantiallythe same manner as described above with reference to FIG. 1 followingthe pre-oxidation rinse 12 where the rinsed sorbent slurry is introducedor mixed with the oxidant/base solution and introduced into continuousflow reactor 14. However, in this embodiment, the dissociated ions ofthe reaction products are retained and processed in the same continuousflow reactor 14, as the solid oxides of manganese particles upon whichthe reaction products formed. Thus, in addition to the solid oxides ofmanganese, the regeneration slurry being processed in reactor 14 willalso contain disassociated reaction product ions.

If the reaction products are manganese salts, e.g., manganese sulfate(MnSO₄) and manganese nitrate (Mn(NO₃)₂), then Mn⁺², SO₄ ⁻², NO₃ ⁻¹,spectator ions, suspended solids or other particulates will be in theregeneration slurry solution. While the solid oxides of manganese arebeing regenerated, the Mn⁺² ions are at the same time being precipitatedout of solution as newly formed oxides of manganese. As in theregeneration method illustrated in FIG. 1 and discussed above, thesolution temperature and pressures are maintained and controlled to bewithin the boundaries of the MnO₂ stability window at the prescribedoperating or processing temperature and pressure. Similarly, theregeneration slurry is metered through the orifice and conditions in theslurry are monitored and adjusted with respect to temperature, pressure,Eh, and pH, as necessary, to move and maintain conditions within theMnO₂ stability area as processing proceeds in continuous flow reactor14. The end product is a combination of regenerated and precipitatedoxides of manganese having high oxidation states and/or high orincreased pollutant loading capacities. The solid sorbent particles may,in part, serve as substrates on to which newly formed MnO₂ isprecipitated. In all other respects processing and handling of thecombined regenerated and precipitated sorbent follows that as abovedescribed with regard to FIG. 1.

When a pre-oxidation rinse is employed as in FIG. 1, the pre-oxidationfiltrate contains the disassociated reaction products, including Mn⁺²ions, which can be precipitated out of solution as oxides of manganesewithout solid oxides of manganese particles being present in thesolution. This is depicted in FIG. 3 where the pre-oxidation filtrate isshown being directed to a continuous flow reactor 24 of precipitationsubsystem 30. The precipitation subsystem 30, as depicted includes, thecontinuous flow reactor 24 equipped similarly to continuous flow reactor14, with at least one static mixer or mixing device 15, and probes13A-13D; filtration unit 16; rinse 17; dryer 18 and comminuting device19. As previously discussed above with reference to the systems of FIGS.1 and 2 and the methods practiced therein, the components of thecontinuous flow reactor subsystem 30 and steps of the method of theinvention carried out therein are substantially the same though numbereddifferently and in a some instances termed differently. Nonetheless, thecorresponding system components of the earlier discussed embodiments ofthe systems of the invention shown in FIGS. 1 and 2 and the steps of themethods as described herein above are substantially the same. Thestatements made above regarding the corresponding counterpart componentsof regeneration systems shown in FIGS. 1 and 2 and operating conditionsand parameters (temperature, pressure, Eh, and pH) are equallyapplicable to the components of the precipitation subsystem 30 of FIG. 3and the steps carried out therein. Therefore, they are not repeated herein order to avoid undue repetition. Further, in this embodiment themethod proceeds in a similar manner as described above with reference toFIG. 1 following the pre-oxidation rinse 12 or with reference to FIG. 2.The obvious difference being that no solid oxides of manganese areinitially present in the pre-oxidation filtrate and oxidant/basepre-mixed solution being processed in continuous flow reactor 24.

The pre-oxidation filtrate is heated to or maintained at the operationaltemperatures of about 100° C. or greater, prior to introduction intocontinuous flow reactor 24 and is combined with a preheated aqueouspremixed oxidizer/base solution in the continuous flow reactor 24 is toform a precipitation solution. Utilizing the probes 13A-13D,precipitation solution temperature, pressure, pH, and Eh arerespectively monitored and controlled. As precipitation proceeds,temperature, pressure, pH, and Eh adjustments, as previously describedherein above, can be made as necessary to move and/or maintainprecipitation solution conditions within the MnO₂ stability area as MnO₂precipitation proceeds. The resultant precipitated oxides of manganesewhether dried and comminuted or utilized as a filter cake or slurry willhave oxidation states and/or loading capacities equal to or greater thanthe oxides of manganese originally utilized and upon which the reactionproducts were formed.

Another embodiment of the invention relates to the pretreatment ofvirgin oxides of manganese, whether of the NMD, EMD or CMD type, toincrease their loading capacity and/or their valence state. This meansthat oxides of manganese that otherwise might not be economical for useas a sorbent in, for example, the Pahlman Process™ Technology or otherpollutant removal system or for other commercial applications due topoor loading capacity or low valence states may be made viable for suchuses. The method of this embodiment can be understood with reference toFIG. 4. In this figure, system 10, as depicted, includes a continuousflow reactor 14 equipped similarly to previously discussed continuousflow reactors with at least one static mixer or appropriate agitator 15,probes 13A-13D, filtration unit 16, rinse 17, dryer 18, and comminutingdevice 19, as in FIGS. 1-3. In the interest of avoiding unduerepetition, the components of system 10 in FIG. 4, absent thepre-oxidation rinse 12, are the same components as that of system 10 ofFIGS. 1-3 and that the function and operation of the correspondingsystem components will be the same in both embodiments of the systemsand of the methods of the invention as depicted in FIGS. 1-4. Further,the statements made above regarding the corresponding counterpartcomponents and process steps in regeneration system 10 of FIG. 1 andoperating conditions and parameters (temperature, pressure, Eh, and pH)are equally applicable to the components of system 10 of FIG. 4 andtherefore they are not repeated here. Further, in this embodiment themethod proceeds in substantially the same manner as described above withreference to FIG. 1 following the pre-oxidation rinse 12 where rinsedloaded oxides of manganese are made into slurry, specifically a rinsedsorbent slurry, by the addition of an appropriate quantity of water andintroduced into the continuous flow reactor 14.

Applicants have found that the loading capacity and/or valence state ofvirgin oxides of manganese, both naturally occurring (NMD) and synthetic(EMD and CMD) can be increased through pretreatment according to thismethod. Following the processing steps of the embodiment of the methodof the invention depicted in FIG. 1 following the pre-oxidation rinse,as previously discussed above, excepting that a sorbent slurry of virginoxides of manganese is being introduced into continuous flow reactor 14instead of the sorbent slurry of rinsed loaded oxides of manganese beingintroduced into the continuous flow reactor 14. The resulting pretreatedoxides of manganese may be rinsed, dried and comminuted, as appropriateas described above.

Yet another embodiment of a method of the invention can be understoodwith reference to FIG. 5, which depicts a precipitation system 30according to the invention. The operation of this system issubstantially the same as precipitation subsystem 30 depicted in FIG. 3.The precipitation system 30, as depicted, includes a continuous flowreactor 14 equipped with at least one static mixer or agitator 15,probes 13A-13D, filtration unit 16, rinse 17, dryer 18, and comminutingdevice 19. Again, as previously discussed above with reference to theother embodiments systems of the invention employing a continuous flowreactor 14 and the methods practiced therein, the components of theprecipitation system 30 and steps of the method of the invention carriedout therein are substantially the same though numbered or termeddifferently in some instances. Nonetheless, the corresponding systemcomponents of the earlier discussed embodiments of the systems of theinvention employing a continuous flow reactor and the steps of themethods as described herein above are substantially the same. Thestatements made above regarding the corresponding counterpart componentsof regeneration systems 10 as applied to the precipitation subsystem 30and operating conditions and parameters (temperature, pressure, Eh, andpH) are equally applicable to the components of precipitation system 30of FIG. 5 and the steps carried out therein. Therefore, they are notrepeated here in order to avoid undue repetition. Further, in thisembodiment, the method proceeds in a similar manner as described abovewith reference to FIG. 1 following the pre-oxidation rinse 12 withspecific reference to precipitation subsystem 30 depicted in FIG. 3.Again, no solid oxides of manganese are initially present in solution inthe continuous flow reactor 24.

In FIG. 5, preheated aqueous premixed oxidant/base solution and heatedmanganese salt solution are introduced into continuous flow reactor 24and form a precipitation solution. The preheated premixed oxidant/basesolution is so prepared as to have conditions that, when added at orbefore the orifice plate, move the precipitation solution into the MnO₂stability area. The preheating of the constituent solutions prior tomixture serves to avoid or minimize the precipitation of lower oxides ofmanganese. Utilizing the probes 13A-13D, temperature, pressure, pH, andEh are respectively monitored and thereafter adjusted and maintainedwithin the MnO₂ stability area by introduction of additional oxidizingsolution and base or acid and with temperature and pressure adjustment,all as necessary. The resultant precipitated oxides of manganese whetherdried and comminuted or utilized as a filter cake or slurry will havehigh or increased loading capacities and/or valence state that are equalto or greater than that of commercially available NMD, EMD and CMD.

Precipitated oxides of manganese, whether formed in precipitationsubsystem of FIG. 3 or FIG. 5 may be filtered, decanted or otherwisecollected and dried. If further oxidation of the precipitated oxides ofmanganese is required, the drying step may be carried out in oxidizingatmosphere. Alternatively, in accordance with the methods of theinvention, an additional oxidizer, as previously described may beintroduced into continuous flow reactor 24 while the oxides of manganeseare being formed and precipitated. For example air or oxygen can bebubbled through or a persulfate or other suitable oxidizer may be used.As the oxidation and precipitation of the manganese ions occurs aspreviously discussed in this application, the newly precipitated oxidesof manganese have a valence state close to 4+ and an oxidation strengthin the range of 1.5 to 2.0, preferably 1.7 to 2.0, and has a BET valueranging from about 1 to 1000 m²/gr. With comminuting, oxides ofmanganese particles can be sized for industrial and chemical applicationuses and particularly a particle size ranging from 0.5 to about 500microns and be sent to the sorbent feeder for reuse in removal of targetpollutants.

During processing according to the invention, valuable and recoverableanions, such as sulfate, nitrate, and chloride will be present infiltrates, for example in the pre-oxidation, oxidation filtrate andregeneration filtrate as shown in FIG. 1, the oxidation and regenerationfiltrates shown in FIG. 2, the oxidation and precipitation filtratesshown in FIG. 3, and the oxidation and pretreatment filtrates shown inFIG. 4. The filtrates from the water used in the rinses may be utilizedfor a number of cycles before the spectator ion concentrations reachlevels meriting their recovery.

When using oxides of manganese to capture SO_(X) and/or NO_(X), sulfate,and nitrate, reaction products and their corresponding anions will bepresent in filtrates. They may also be present as well as other anionsand cations from the oxidizers, acids and bases used. Sulfate andnitrate byproducts as well as others that may be formed from otherspectator ions formed, separated or processed from the variousfiltrates.

Ion exchange can be utilized as a mechanism for the separation andrecovery of useful sulfate and nitrates. The dissolved sulfates andnitrates of manganese in the pre-oxidation filtrate can be processed inanion exchangers, permitting the recovery manganese cations andseparation of the sulfate and nitrate anions. To accomplish thisseparation, the pre-oxidation filtrate, containing dissolved sulfatesand nitrates, is passed across or through a bed or column of an anionexchange resin that has an affinity for at least one of the two anionsto remove those anions. The resin will absorb the anion, for instancethe sulfate, while permitting the nitrate to pass through the bed orcolumn. Additionally, the solution stripped of sulfate can then bepassed across or through a second bed or column of yet a second anionexchange resin having an affinity for the nitrate thereby capturing thenitrate. After the resin is loaded, the vessel or vessels containing theresin can be taken off-line and the resin therein stripped of thecaptured anion and recovered for reuse.

Suitable anion exchange resins and vessels are known to and readilyidentified by those skilled in the art. For purposes of illustration,the anion exchange resin may have a halogen, for example a chloride, inthe exchange position on the resin. By passing a solution containmanganese cations and sulfate and/or nitrate anions over the resinchloride anions are eluted and exchanged for sulfate and/or nitrateanions. The solution, after passing through the anion exchanger orexchangers in series, will contain manganese chloride from whichmanganese carbonate or manganese hydroxide is precipitated with theaddition of a soluble carbonate or hydroxide compound; and oxides ofmanganese as previously described in the discussion of the production ofoxides of manganese from the pre-oxidation filtrate. The sulfates and/ornitrates loaded on the resin can in turn be eluted with a solutioncontaining chlorides of potassium, sodium or ammonium in order togenerate useful sulfates and nitrate by-products for marketing orfurther processing. The filtrates and rinse solutions left over afterprecipitate formation can be utilized for this purpose.

The solubility of manganese nitrate is greater than 1.5 times thesolubility of manganese sulfate. Solubility of the nitrate is 61.7 masspercent of solute at 250° C., whereas the solubility of sulfate is 38.9mass percent of solute at 250° C. (Handbook of Chemistry and Physics.)Fractional crystallization, a separation technique known to thoseskilled in the art, can take advantage of the solubility difference toisolate nitrates of manganese and sulfates of manganese from thepre-oxidation filtrate. The filtrate may be cooled and/or evaporated tocause the crystallization of the lesser soluble manganese sulfate whichcan then be harvested as solid crystals. The solution remaining can berecycled to pre-oxidation rinse 12 for reuse. Once the concentration ofmanganese nitrate is sufficiently high, the solution aftercrystallization of sulfates is further cooled and/or evaporated tocrystallize the nitrates which can then be harvested as solid crystals.Alternatively, the solution can be processed with hydroxides orcarbonates, as previously described herein above, to generate oxides ofmanganese and marketable nitrate by-products.

Another variation upon the methods of the invention would utilize thedifference in thermal decomposition temperatures of nitrates andsulfates of manganese. Nitrates of manganese are reported to decomposeat temperatures between 140° C. to 450° C. to form NO and oxides ofmanganese. However, sulfates of manganese are understood to liquefy atelevated temperatures but in the presence of trace amounts of a reducingagent, e.g., carbon monoxide or hydrogen, they decompose to SO₂ and MnOwhich when further heated in an oxidizing atmosphere form oxides ofmanganese. Reacted sorbent loaded with both nitrates and sulfates ofmanganese may be heated, prior to introduction into either continuousflow reactor 14 or pre-oxidation rinse 12, in an oxidizing atmospherewhereupon manganese oxide is formed and nitrogen dioxide and/or sulfurdioxide are desorbed and captured. If both reaction products are to bethermally desorbed, the reacted sorbent may be heated to and maintainedat a first temperature at which nitrates of manganese, primarily, if notexclusively, desorb. The temperature could then be elevated to desorbthe sulfates of manganese loaded on the sorbent. Whether one or bothreaction products are desorbed, the oxides of manganese may then beprocessed in continuous flow reactor 14 as described herein above andthe desorbed gas or gases captured and further processed. If thenitrates are first thermally desorbed, the sorbent may be routed eitherthrough a pre-oxidation rinse or routed directly to an oxidation vessel14. The recovery of useful sulfate by-products would be as previouslydescribed from either a pre-oxidation filtrate or an oxidation filtrate.

As previously mentioned oxidizer or oxidizing solutions can be formedon-site in an electrolytic cell utilizing process streams generated inthe methods of the invention. FIG. 10 depicts electrolytic cell 72 usedfor oxidant production and by-product production along with otherbeneficial integrated functions that may be used in the Pahlman Process™Technology or other pollutant removal system. Given the cost of oxidantsand the ion values left in the process streams of the invention, itwould be useful and highly advantageous to produce oxidants or oxidizerson-site in electrolytic cell 72 and not purchase them for one time useas it would be prohibitively expensive.

As illustrated in FIG. 10, the Electrolytic Cell and By-Productsdiagram, oxidant production system 70 includes electrolytic cell 72.Electrolytic cell 72 has an anolyte compartment 74 with a vent, apositively charged anode 75, a catholyte compartment 76 with a vent, anegatively charged cathode 77, a diaphragm (not shown) dividing theanolyte compartment 74 and the catholyte compartment 76. Oxidantproduction system 70 further includes a mixing tank 78, a cooler (notshown), a filter/dryer unit 79, an evaporator 80, an anolyte holdingtank 82 and oxidant dissolving tank 84.

Filtrate solutions containing useful values, such as those shown comingfrom the rinses and filtration units in FIGS. 1-9 and shown beingdirected to by-products processing vessel 66, in FIGS. 7-9, may containions from reaction products, such as sulfates, nitrates, and chlorides,from oxidants, bases and acids, and other constituents such as heavymetals. The filtrate solution, containing sulfate anions for example, isrouted to the catholyte compartment 76 where it comes in contact withthe cathode 77 that is negatively charged with a direct current (DC)voltage. At the same time, a solution of ammonium sulfate containedwithin the anolyte holding tank 82 is routed to the anolyte compartment74 where it comes in contact with the anode 75 that is positivelycharged with a direct current (DC) voltage.

The ammonium sulfate is purchased and brought in to charge the anolytecompartment and is a closed loop that will from time to time needmakeup. In electrolytic oxidation, the sulfate (SO₄ ⁻²) anion componentof the ammonium sulfate (NH₄)₂SO₄ within the anolyte compartment 74 isconverted to an ammonium persulfate (NH₄)₂S₂O₈. Some of the now freeammonium ions migrate across the diaphragm to the catholyte compartment76. There will be migration or leakage of cations and anions across thediaphragm that is between the positively charged anolyte compartment 74and the negatively charged catholyte compartment 76. Nearly all thepotassium sulfate (K₂SO₄) that is formed from interaction between thepotassium cation from previous additions of potassium hydroxide (KOH) inthe system and the stripped sulfate anion from the manganese sulfate(MnSO₄) within the catholyte compartment 76 passes through to the mixingtank 78. There will also be ammonium sulfate or ammonium hydroxide mixedwith the potassium sulfate leaving the catholyte compartment 76depending upon the pH. An acid and or base may be introduced to thecatholyte compartment 76 to adjust pH and is also used to adjust massbalances of cations and anions. Heavy metals, such as mercury andarsenic as an example, amongst many other kinds of metals, present inthe filtrate will be plated out on the cathode or, depending upon the pHof the solution, could precipitate out as an oxide.

Both the anolyte compartment 74 and the catholyte compartment 76 arecontinually being filled and continually drained. The anolytecompartment 74 drains into the mixing tank 78 and the catholytecompartment 76 drains into the mixing tank 78. Ammonium persulfate((NH₄)₂S₂O₈) from the anolyte compartment 74 mixes with potassiumsulfate (K₂SO₄) from the catholyte compartment 76 within the mixing tank78. The electrolytic cell 72 and the mixing tank 78 are cooled with acooler (not shown) to around 15° C. Solutions entering and exiting theelectrolytic cell 72 will be within a few degrees of 15° C. One maychoose to run the electrolytic cell 72 at higher temperatures but thereis reduced efficiency. Due to the solubility differences of ammoniumpersulfate and potassium persulfate it is possible to precipitate outthe potassium persulfate as it has a much lower solubility than ammoniumpersulfate. The liquor containing crystals of potassium persulfate andammonium sulfate in solution is routed to the filter/dryer 79 and thepotassium persulfate crystals are separated from the liquor.

The potassium persulfate crystals may then be dried for sale and aportion of the potassium persulfate crystals may be routed to theoxidant dissolving tank 84. Distillate from the evaporator 80 is routedto the oxidant dissolving tank 84 to dissolve the potassium persulfatecrystals and make a solution that may then be routed for use in sorbentregeneration, pre-treatment, and or precipitation according to theinvention. The solution of ammonium sulfate that has been separated fromthe potassium persulfate in the filter/dryer 79 is routed to theevaporator 80. Through evaporation, the concentration of the ammoniumsulfate is increased to an acceptable point that provides for a highdegree of conversion efficiency into an ammonium persulfate in theanolyte compartment 74. The high concentration of ammonium sulfatesolution in the evaporator 80 is routed to the anolyte holding tank 82to be further routed to the anolyte compartment 74 of the electrolyticcell 72 in a continuing cycle. A polarizer may be used in the anolytecompartment 74 to increase anode efficiency such as but not limited toNH₄SCN.

During the electrolytic process there is electrolysis of water intohydrogen at the cathode and oxygen at the anode. These compounds willexit the vents of their respective compartments of the electrolytic cell72. By adjusting the parameters of the electrolytic cell 72, it ispossible to decompose nitrate ions NO₃ ⁻¹ and vent them from theelectrolytic cell or allow them to pass through the cell unchanged.Other compounds, including but not limited to, chlorides and fluoridesthat are found in industrial process gas streams that get removed in thesorbent capture and regeneration system may be vented from the catholytecompartment 76 or the anolyte compartment 74 during the operation of theelectrolytic cell as a gas or allowed to pass through depending on theoperating parameters of the e-cell. This is one way to separate themfrom the by-products that are being created, although not the only way.This would avoid having to separate anions that are not compatible toby-product operation and sales. It is desirable to use acids and basesthat have compatible ions and cations. For example, potassium hydroxidewould be used with potassium persulfate or potassium sulfate. Likewise,a compatible acid to go with these would be sulfuric acid (H₂SO₄). Thisgreatly aids in by-product separation from pregnant liquors. Other typesof electrolytic cells may be incorporated in the process to formoxidants. Such electrolytic cells include, but are not limited to, anundivided cell without a diaphragm which may be used to producepersulfates and other oxidants or a multiple divided cell with severaldiaphragms may be used. Those skilled in the art of electrolytic cellswould be able to select a cell design most beneficial to the particularoxidant being produced, to the economics of production, and to themaintenance requirements.

Applicants use sulfate containing filtrate solution and ammoniumsulfates for purposes of illustrative explanation of the operation andmethod of production in an electrolytic cell. It should be understoodthat the filtrate may contain different ion constituents from whichdifferent oxidants, such those earlier identified herein, may be made.Again, attention to compatibility may ease processing when certainby-products are to be formed.

The above-described oxidant production methods may be combined withother processing steps to produce useful and marketable by-products fromthe values in the filtrates and rinse solutions routed to a by-productsvessel. For example, manganese oxides or useful salts may be produced.The ability to produce oxidants from the process streams may eliminateor reduce cost of purchasing commercially available oxidants for use inthe methods of the invention.

A derivation of an electrolytic cell, an internal electrolytic cell mayoptionally be installed within the tube or pipe of the continuous flowreactor section before the backpressure regulator or similar device anddownstream of the static mixer. This optional use of electrolytic celltechnology could be applied to all embodiments of the Applicant'sinvention that utilize a continuous flow reactor for the precipitationregeneration and pretreatment of oxides of manganese. Operation of theinternal electrolytic cell would be conducted as one skilled in the artof electrolytic process would have knowledge. There would be cathodesand anodes within the tube or pipe of the continuous flow reactor and,as consistent with the first embodiment, the continuous flow reactor canbe maintained and controlled to specific temperature, pressures, pH, Eh,molarities, and viscosity set points that serve to keep the conditionswithin the continuous flow reactor within the MnO₂ stability window andconducive to sorbent flowing through the reactor. The high currentdirected across the cathodes and anodes helps provide beneficialcharacteristics to the sorbent particle, increases the yield of MnO₂ andincreases sorbent loading capacity and/or oxidation strength. A benefitof integrating an internal electrolytic cell into a continuous flowreactor is that less oxidant may be required to provide the necessarysolution Eh and oxidant could also be regenerated in situ. An addedbenefit would be lower equipment costs for moving sorbent and solutionsin the process. The polarity of the cathodes and anodes can be reversedat a particular frequency if necessary to prevent and/or release anysorbent buildup; or as in EMD production in electrolytic cells, anautomatic electrode cleaning device may be installed.

Use of sonic energy during processing, particularly during precipitationmay favorably affect the performance of the metal oxides produced in thevarious embodiment of the invention. As an example, a custom sonic probemanufactured for the continuous flow reactor was used in one experimentto produce sorbent. A fixed frequency was utilized and sorbent wasproduced according to the differing embodiments of the Applicantsinvention. An MnO₂ sorbent was produced using potassium as the foreignmetal cation. The surface area as measured in square meters per gramaccording to the B.E.T. method was 373 m²/gr. Producing the same sorbentunder the same conditions without sonication resulted in a reduction insurface area to 263 m²/gr. Not to be limited by the example, if thetarget pollutant capture with metal oxide sorbent is primarily a surfacearea reaction mechanism than increased surface area would lead toincreased sorbent utilization, as is the case in NOx and Sox pollutantcapture rates. Sonic energy, as applied industrially, includes the rangefrom ultrasonic, which is short-wave, high-frequency (greater than20,000 Hz.) energy, to infrasonic, which is long-wave, low-frequency(less than 20 Hz.) energy. All forms of sonic energy are transmitted aspressure waves, and are usually generated by specialized devices ortransducers that convert electricity into sonic energy within thedesired frequency range.

Industrial applications of ultrasonic energy include agitation of liquidsolutions for applications such as solvent parts cleaning for example.Infrasonic acoustic energy, for example, is used to loosen material indry powder transport systems, to promote smooth flow and preventstoppage of the material, or to remove filter cake from bag-typefilters; it is not typically used in liquid applications. These andother applications of such technology may also be methods oftransferring energy to a solution, gas, or solid material, withoutraising its temperature. Sonic energy can be utilized in embodiments ofboth batch and continuous flow reactor methods of metal oxideprecipitation from a metal salt, metal oxide regeneration, and virginmetal oxide treatment according to the invention.

There are many commercial manufacturers of ultrasonic equipment such assmall or laboratory scale ultrasonic equipment like those available fromthe Cole-Parmer Instrument Company and large scale equipment, such ashigh pressure and/or high temperature devices available from Misonix.

With the application of sonic energy in the form of ultrasonic orinfrasonic waves has improvements in sorbent activity or loadingcapacity can be achieved. The application of sonic energy duringprocessing of metal oxides may be doing all or some of the followingactions: (1) enhancing agitation during sorbent processing in thecontinuous flow reactor to improve reaction rates and enhance mixing;(2) promoting rapid dissolution of reaction products from loaded sorbentsurfaces during regeneration; (3) increasing dissolution rates ofchemicals used in the processing of metal oxides; (4) alteringstructural development of crystal structure during and followingprecipitation from solution; (5) breaking up large metal oxides crystalformations; and increasing surface area without decreasing particlesize. In the methods and systems of the invention, sonic energy would begenerated by specialized devices or transducers and directed which mayoptionally be incorporated into the vessels or continuous flow reactor,for example. Such sonication devices may be used and incorporated intoother system components, such as oxidant, acid or base vessels or vesselin which manganese salts are mixed with water prior to precipitationprocessing.

The precipitation methods of the invention may also be carried out inthe presence of a magnetic field to enhance sorbent characteristics.Metal oxides and foreign metal cations have paramagnetic properties thatcan be manipulated in a magnetic field to enhance or facilitateincorporation of foreign metal cations into the crystalline structure ofmetal oxides. This may result in high surface areas and greaterpollutant capture rates and/or loading capacity, to name a few of thebenefits of precipitation in the presence of magnetic fields. The use ofmagnetic fields may be conducted concurrently along with other processapplications or steps, such as sonication by way of non-limitingexample.

In addition to forming metal oxides in a continuous flow reactor,Applicants have developed systems for preparing metal oxides of theinvention using batch processing system.

As further discussed below heated oxidizing solutions having the desiredpH-Eh-temperature combination can be prepared and maintained or adjustedby increasing or decreasing oxidizer, acid or base concentrations and/ortemperature adjustment, as appropriate, so that the initially adjustedor prepared to be in the polyatomic ion, metal ion, co-precipitation,and/or metal oxide stability area. With monitoring of Eh, pH, andtemperature, an operator can make necessary adjustments in order tomaintain or return the oxidizing solution to conditions within the metaloxide stability area or co-precipitation stability area. Such monitoringand adjusting can also be automated utilizing electronic probes orsensors and controllers as discussed later herein below.

As discussed with respect to the continuous flow reactor, the batchreaction systems of the invention may be used in regeneration,pretreatment and precipitation of desired metal oxides. Precipitationwill be the focus of the discussion of the batch systems, but all ofthese processes are carried out with the use of similar oxidationvessels; agitation devices and probes for temperature, Eh and phmeasurement with which the oxidation vessels are equipped, filtrationunits, and rinses. The oxidation vessels are also equipped with a heater(not shown in the figure hereof) for adding heat to and maintaining thetemperature of the solutions in the vessels. For applications requiringdried oxides of manganese, a dryer would be another common component.And, for applications requiring the oxides of manganese to be comminutedand sized, a comminuting device would be another common component. Thesecomponents are further discussed herein below.

For this example, manganese will be used as an exemplary metal with theunderstanding that other metals may be processed with similar attentionto stability areas and the other aspects of the invention. Turning toFIG. 6, a manganese salt solution is added to a precipitation vessel 54that is equipped with an agitator 55, also referred to herein as anagitation means 55. Any of various agitation devices known to thoseskilled in the art to be suitable for agitating, mixing and stirring thesolid-liquid slurries so as to keep the solid oxides of manganeseparticles that are formed generally suspended in the solution can beutilized. As illustrated in FIG. 6, vessel 54 is optionally equippedwith temperature probe 13A, pH probe 13B, and Eh probe 13C. These probesare utilized to measure their respective parameters in the heatedaqueous oxidizing solution and may be in electronic communication with acontroller to provide automatic control of the system. The manganesesalt solution may additionally include foreign metal cations which maybe added as other metal salts in the desired concentrations that caneither be dispersed through the structure of the primary metal oxide, inthis example oxides of manganese, or co-precipitated as a metal oxidecompound If conditions are allowed to move into a co-precipitationstability area of oxides of manganese and of the metal or metals of theforeign cations.

In the vessel 54, the manganese salt solution is mixed with a heatedoxidizing aqueous solution therein. The heated aqueous oxidizingsolution is preferably preheated to temperatures at or near the boilingpoint of aqueous solutions at atmospheric pressure. For example, at sealevel, this would be about 100° C. Precipitation may be carried out attemperatures ranging from about 90° C. to about 110° C., withtemperatures between 95° C. to about 108° C. being preferred, andtemperatures between about 100° C. to about 105° C. being more preferredat sea level atmospheric pressures. The solution temperature should bemaintained unless a temperature adjustment away for near boiling isrequired in order to maintain the aqueous solution system with the MnO₂stability area as other system parameters shift during processing. Theoxides of manganese may also be precipitated within an enclosed systemso that the temperature may be increased above 100° C. and the pressuremay be above atmospheric. Determining which parameter adjustments tomake is a matter of engineering or operator choice and may be based uponeconomic considerations as long as the adjustment moves systemconditions into or maintains those conditions within the MnO₂ stabilityarea.

For the manganese salt solution, the heated aqueous oxidizing solutionprovides the required electrochemical (oxidizing) potential (Eh), withinthe specified temperature and pH range to yield precipitated oxides ofmanganese having high loading capacities and/or high oxidations states.Under agitation, the slurry formed in the precipitation vessel 54 iscontinuously mixed and the pH of the slurry is adjusted by appropriatemeans, e.g., addition of acid or base. The precipitated oxides ofmanganese are allowed to remain within the slurry for a time sufficientto achieve an increased oxidation state and/or a target pollutionloading capacity equal or greater than that of virgin oxides ofmanganese. At or near the sea level atmospheric pressures, a sufficienttime may be between about a couple of minutes to about 70 minutes ormore, preferably between about 1 minute to about 45 minutes, and morepreferably between about 1 minute to about 10 minutes. This time mayvary in enclosed systems operated at temperatures above 100° C. andpressures above atmospheric. Such processing times are rapid compared tothe hours and tens of hours of sometimes staged processing of prior artmethods. At atmospheric pressures, Applicants have found that an optimaltime for the solid rinsed oxides of manganese to remain in theprecipitation vessel 54 is approximately 10 minutes, during which timethe precipitated oxides of manganese are oxidized up to valance statesclose to +4. A deviation of two to three minutes above or below 10minutes is near enough to optimal to provide precipitated oxides ofmanganese having oxidation states and/or loading capacities particularlysuitable for use as a sorbent for target pollutant removal and otheruseful applications. It being understood that with greater deviationsfrom the optimal time but yet within the above stated time ranges oxidesof manganese suitable for pollutant removal (particularly when highloading capacity is not required) and for other uses may nonetheless beproduced with the invention.

Once the metal oxides are removed from the batch reaction systemoxidation vessel they may be processed in the same way as describedabove with respect to the metal oxides produced in the continuous flowreactor.

Embodiments of the methods of the various embodiments of the inventioninvolve and employ Applicants' recognition that metal oxides processedin aqueous systems in which conditions and parameters are adjusted andmaintained within the metal oxide stability area will yield metal oxideshaving high pollutant loading capacities and/or high oxidation states.Further, they employ Applicants' recognition that the desirablecharacteristics of metal oxides processed according to embodiments ofthe methods of the invention can be beneficially manipulated or adjustedwith introduction of foreign cations into process solutions. The use offoreign metal cations in the sorbent precipitation methods of theinvention lead to incorporation of these cations into the structure ofthe oxides of manganese and can change sorbent characteristics such asparticle size, shape, bulk density, surface area (BET), pore volumes,porosity, crystalline structure, morphology, electrochemical oroxidation potential, valence state, and other sorbent characteristicsbeneficial to the removal of target pollutants. This is illustrated inlater discussion of Example 1 and Table 2 below. More than one foreignmetal cation maybe used depending upon the characteristics that arerequired in an application. Thus, with the methods of the invention,metal oxides can be engineered for optimal or specific requirement indifferent applications.

In its various embodiments, the invention and the methods and systemsthereof also provide for rapid, adaptive and stable processing of metaloxides incorporating foreign cations; more specifically they provide forthe precipitation of such metal oxides. Metal oxides thus processed aresuitable for use as a sorbent in dry and wet gaseous pollutant removalsystems, aqueous pollutant removal systems, respirators, batteries, andother applications demonstrated by Applicants or known to those skilledin the art.

Without being bound by theory, Applicants believe that processing metaloxides according to the invention in a heated aqueous oxidizing solutionsystem maintained within a metal oxide stability area orco-precipitation stability area may beneficially affect a number ofcharacteristics of the oxides of manganese, as an example. Suchcharacteristics include, but are not limited to, particle size andshape, crystalline structure or morphology, porosity, composition,surface area (BET), bulk density, electrochemical or oxidation potentialand/or manganese valence states. Some or all of these characteristicsaffect the performance of oxides of manganese in their various uses and,particularly, in their use as a sorbent for removal of gaseouspollutants.

Further, Applicants believe that with the introduction of foreigncations, metal and/or non-metal, into oxides of manganese, thecharacteristics can be further enhanced, adjusted, controlled orengineered. Foreign metal cations useful in the precipitation andco-precipitation of oxides of manganese according to the inventioninclude, but are not limited to, those metals known as representativeand transition metals, such as iron, titanium, barium, lithium,magnesium, sodium, potassium and aluminum, to name a few. Further, rareearth metals, alkali metals, noble metals and semi-conductive metals mayalso be processed in the methods and systems of the invention. Metalcations particularly useful in the co-precipitation method of theinvention are those that enhance the removal ability of a first metaloxide or that themselves form stable metal oxides, second or other metaloxides, which in turn, preferably but not necessarily, form eithersoluble or thermally decomposable metal salts when reacted with targetpollutants in a gas stream. Metal oxides that can yield reactionsproducts with these desired properties include, but are not limited to,both representative metals and transition metals. Of, the transitionmetals those from the fourth period of the periodic table areparticularly well suited. Suitable metal oxides include, but are notlimited to, oxides of any one of the following metals: magnesium,calcium, scandium, chromium, manganese, iron, nickel, copper, zinc,aluminum, yttrium, rhodium, palladium, silver, cadmium and combinationsthereof. These and other metals may form high valence metal oxidesthemselves or be integrated into the lattice structure of a primarymetal oxide through controlled addition during embodiments of methods ofthe invention. If the foreign metals are not oxidized to a high valencestate, they may still be useful as foreign metals in a hydroxide orlower valence metal oxide form. Other metals that may be useful in someform as a foreign metal include but are not limited to cobalt, platinum,molybdenum, vanadium, and nickel.

Other metals may be integrated with the primary or first metal oxides ofembodiments of the invention in at least two ways: co-precipitation andthrough the controlled introduction of foreign cations into the metaloxides. Co-precipitation refers to precipitation of at least first andsecond metal oxides as a metal oxide compound. To accomplish this,solution conditions described in embodiments of the methods of theinvention relating to metal oxide production are maintained in a regionon the appropriate Pourbaix diagram where the metal oxide stability areaof a first metal oxide overlaps with the metal oxide stability area orareas of one or more other metal oxides.

With reference to FIGS. 12-14, if one were to use iron and manganese,for example, there is a portion of the iron oxide (Fe₂O₃) stability areain its Pourbaix window of FIG. 13 that will also overlap the MnO₂stability area in the Pourbaix window for MnO₂ of FIG. 12. The area ofoverlap is the co-precipitation stability area and can be seen in FIG.14 as delineated by a light or gray line above “MnO₂{S}” and the lowerdark or black line below “MnO₂{S}”. More than one other metal cation canbe used and multiple other metal oxide stability areas can be overlappedif one wants to form a metal oxide compound of more than two metaloxides, have more than one other metal oxide precipitated along with thefirst metal oxide. As an example, one may use aluminum and iron whenco-precipitating MnO₂. These and other metal oxides may also be used asa substrate onto which MnO₂ or other metal oxide is precipitated andsupported. When MnO₂ is precipitated onto a substrate such as particlesof a second metal oxide, the substrate is added into the metal saltmixture from which the metal oxides are precipitated. Alumina or othermetal oxides substrates of various sizes and shapes, e.g., particles,pellets or other structures may be used as substrates. The substratesmay be mixtures of more than one metal oxide. Additionally, thesubstrate may be a filter medium or other structure that may be utilizedfor pollutant removal in different pollutant removal systems employingsuch filter media or structures, e.g., aqueous filtration systems forindustrial or residential applications or respirators.

The incorporation of foreign metal cations occurs when foreign metalcations are bound within the primary metal oxide crystalline structureduring precipitation. Sorbent particle size may also be controlled byusing different foreign metal cations in the sorbent regenerationprocess as their presence in the solution and within the metal oxidecrystalline structure can impact sorbent particle size. The atomicradius differs between metal cation species resulting in differingparticle sizes in the oxides of manganese into which they areincorporated. Also, when spray dryer or spray injection type feeders areused in a gaseous pollutant removal system, adjusting nozzle atomizingair can produce different sorbent particle sizes. The use of foreignmetal cations may provide for an increased utilization of the sorbentfor gaseous or aqueous target pollutant removal, respiratorapplications, batteries, and other applications for metal oxides. It isalso recognized that the presence of a foreign metal cation in theprecipitation solution, while not necessarily being captured within theprimary metal oxide structure, may nonetheless caused increasedutilization due to its reactivity or presence within the combined mixedprocessing solution during precipitation. Increased utilization can beachieved by selecting which foreign metal cation or cations to useand/or increasing the amounts of the particular metal cations usedwithin the metal oxide structure. Foreign metal cations can increase thereactive properties of the sorbent that are directly related tocapturing targeted pollutants or sorbent utilization in otherapplications.

One example of the utility of foreign metal cations is the use of oxidesof manganese in gaseous pollutant removal. By inserting specific foreignmetal cations, such as titanium, into the MnO₂ structure the utilizationratios between SO_(X) and NO_(X) can be changed. The NO_(X) utilizationcan be increased without increasing the SO_(X) utilization. Thus,sorbent can be selectively engineered to increase its utilization oraffinity for different pollutants, and may be selectively engineered todecrease its affinity or utilization for different pollutants. Thismakes for a more cost efficient pollution control system as dependingupon what pollutants are to be captured. The pollutant with the lowestutilization will be the controlling factor in determining how muchsorbent is used in the system. This will affect component sizing, thusreducing capital, and O & M costs. Selective engineering may also beadvantageously utilized in dual-stage or multi-stage removal systemswhere different pollutants are to be serially removed in differentreaction zones and other applications not limited to gaseous pollutantremoval.

In further embodiments, metal oxides are precipitated onto substratesaccording to the processing methods disclosed herein. These substratescould be chemically active or inert. Substrates useful in embodiments ofthe invention include, but are not limited to, activated alumina,activated carbon, silica, resin beads, and other metal oxides. Theprecipitation can take place in a continuous flow reactor or a batchreactor system. The substrate may be added to the metal source solutionand acts as a seed surface upon which metal oxides may precipitate. Themetal oxides may form as layers on the surface of the substrate, asolid-solid mixture of substrate and metal oxides on the surface of theparticle, or a solid-solid mixture substantially throughout the producedparticle. More than one substrate may be used at one time, and one ormore substrates may be used with one or more metal oxides that areco-precipitated with attention to a co-precipitation stability areaand/or with foreign metal cations that are introduced into the metaloxide in a controlled fashion.

One example of a useful application of substrates with the metal oxidesof embodiments of the invention is the precipitation of oxides ofmanganese onto activated carbon for use in aqueous treatment media. Theactivated carbon in this example may act as a seed surface on which theprecipitated oxides of manganese form. It is believed that oxides ofmanganese may form as a layer on the surface of the particle, asolid-solid mixture of activated carbon and oxides of manganese on thesurface of the particle, or a solid-solid mixture substantiallythroughout the produced particle. This is largely dependent on theporosity of the original particle, the concentration of the manganesesalt solution, and the reaction kinetics as influenced by the variousreaction parameters. The resultant precipitated oxides of manganesewhether dried and comminuted, utilized as a filter cake or slurry, orcompacted into a solid contactor element and dried will have high orincreased loading capacities and/or valence state that are equal to orgreater than that of commercially available NMD, EMD and CMD. Theprecipitated oxides of manganese will also have a second active sorbentincorporated therein that may be active in removing other pollutants inaqueous streams known to be removed by activated carbons.

In another embodiment of the invention, the wet metal oxides may becompacted into a solid contactor element and then dried rather thanbeing dried and comminuted after production. This compaction could occurafter filtration but while surface water is still present on the wetmetal oxides. An exemplary method of compacting the oxides of manganeseis to feed the wet solid particles into an extrusion die and force themthrough the die with a feed screw. A feed screw may be a conveyorcomprising a solid core and coaxial helical flights.

The extrusion die could be of any cross-sectional size desired, and ahollow cylindrical extrudate could be produced by having a cylindricalelement extend through the die from the core of the feed screw. Theextrusion die is preferably constructed of a hard material to resistabrasion by the metal oxides, and is preferably polished to a smoothfinish for minimizing friction resistance while compacting the material.Backpressure to improve compaction of the material could be provided bydesigning the die with a slightly decreasing cross-sectional area toprovide for compaction of the material as it passes through the die.Alternatively, backpressure could be provided by elements external tothe die that restrict the movement of the extrudate from the die.Examples are rollers that apply resistance, strap arrangements that canbe controllably constricted around the extrudate, or a controllablecompression donut, each of which can control the rate of extrudateleaving the die and thus the compression pressure within the die.Alternatively, a feed auger that forces the material to be compactedinto the feed screw could be used in conjunction with, or instead of,the exemplary backpressure controls just described, or others, to applyand control pressure within the extrusion die.

The compression of the material may be optimized around severalperformance parameters. First, the material should be sufficientlycompacted so as to meet the demands of handling and the filtrationenvironment without unacceptable levels of mechanical breakdown orsorbent attrition in the process. The material must also be sufficientlycompacted so as to prevent channeling through the solid contactorelement that would result in pollutant bypass or breakthrough andunderutilization of the sorbent within the solid contactor element.Finally, the material must not be compressed to the point that itsporosity is too low. This may result in excessive pressure drop acrossthe solid contactor element, which can create excessive energy demandand operating cost, capital cost associated with more powerful pumps,and mechanical breakdown of the solid contactor element itself due tothe pressure exerted upon it.

Factors that influence the ability to meet solid contactor elementperformance expectations with an extrusion type contactor includeextrusion rate, heating and cooling rate, if applicable, dimensions ofthe extruder screw and die, intrinsic backpressure in the die,externally applied backpressure or feed pressure, particle size andcrush resistance of the various materials, and others which will beobvious to those skilled in the art.

Alternatively, the metal oxides could be compacted by use of apressurized mold or press combination. A hollow mold with an interiorthat is the desired shape of the solid contactor element is employed.The hollow mold has at least one opening. This mold may be filled withmaterial to be compacted. A powered press sized to a tight tolerancewith the mold opening compresses the material to form the solidcontactor element. The solid contactor element can then be removed fromthe mold. Alternatively, the mold may be sized larger than the size ofthe ultimately produced solid contactor element. In this case theproduct of the mold may be machined to the desired shape, on a lathe forexample.

Exemplary mold press operations include vertically oriented molds thatare filled from the top and compressed from the top by the press. Aftercompression the solid contactor element is ejected out the top of themold by an ejector located at the bottom of the mold. In theseembodiments, the mold diameter may be slightly larger at the top toallow for ejection of the molded product. Alternatively, horizontallyoriented molds may be used that have openings on the top for addition ofmaterial. The mold also has a horizontally disposed opening throughwhich the press enters. The press enters the mold from the side andpushes the material past the top opening, effectively closing off thetop opening, and into a horizontally disposed mold where it iscompressed. As the press is retracted the solid contactor element ispushed out of the mold and the next batch of material enters through thenow open top opening.

If the metal oxides to be compacted contain excessive water, provisionmay be made in the compaction process for water removal. This may beaccomplished through submicron sized holes in the extrusion die orcompression mold. It may also be accomplished by a progressive sequenceof compression through a die or a compression mold, a drying step, andthen further compression. This sequence may be repeated if necessary.After the oxides of manganese are compacted, by whatever means, they maybe further dried to form a solid contactor element.

A solid contactor element can be used in conventional water filtrationsystems, water bottles, or other applications and provides a convenientmeans to install and replace filtration media comprising highly activemetal oxides. The filter element also provides for a simple pollutionremoval system with little to no migration of the sorbent through thetreated water system due to the high mechanical integrity of the solidcontactor element. Solid contactor elements can alternatively be formedwith additional sorbent constituents with the metal oxides acting as abinder, from dry particulate metal oxides and an added binder, or fromparticulate metal oxides, additional sorbents, and an added binderand/or reinforcing materials as enabled by examples described below.

It has been found that the co-precipitation of foreign metal cations asdescribed above can enhance the formation of a solid contactor elementconsisting essentially of metal oxides. Also, by inserting a specificmetal cation into the metal oxide structure different adhesive qualitiescan be achieved. Sodium as an example yields a much more dense and hardsolid contactor element than potassium. One may also achieve variousranges of compactness and adhesiveness by changing the amount and typeof metal cation. Porosity, adhesiveness of materials used, hardness,brittleness, ductility, potential for material contraction, amounts andtypes of pollutants captured, and other parameters may be controlled byamounts of activated metal cations coprecipitated with the metal oxidesused to make solid contactor elements. Similar changes in physicalproperties can be controlled by adding other constituents as describedbelow in combination with coprecipitated foreign metal cations. Also,the precipitation of metal oxides onto active or inactive substratesallows for control of the same physical properties of the solidcontactor element and may be used in combination with coprecipitatedforeign metal cations and/or other added constituents to effect changesin physical properties.

In another embodiment, a separate binder may be added to dry or wetparticulate metal oxides or sorbent mixtures. In one embodiment thebinder could be a thermoplastic that is mixed, in particle form, withthe particulate sorbent or a sorbent mixture. This mixture is thencompacted as described above or in any other way known in the art.During the compaction, the temperature may be raised enough to melt thethermoplastic but not so high as to decompose or otherwise impact thedesirable characteristics of the sorbent or other elements in themixture. As the compacted filter element is formed it is cooled to setthe thermoplastic and form a solid contactor element impregnated, orlargely consisting of, metal oxides or a mixture of metal oxides andother sorbents. Suitable thermoplastics for use in this process include,but are not limited to, polyolefins such as polyethylene, polypropylene,polybutene-1, and poly-4-methyl-pentene-1; polyvinyls such as polyvinylchloride, polyvinyl fluoride, and polyvinylidene chloride; polyvinylesters such as polyvinyl acetate, polyvinyl propionate, and polyvinylpyrrolidone; polyvinyl ethers, polyvinyl sulfates, polyvinyl phosphates,polyvinyl amines; polyoxidiazoles; polytriazoles; polycarbodiimides;copolymers and block interpolymers such as ethylene-vinyl acetatecopolymers; polysulfones; polycarbonates; polyethers such aspolyethylene oxide, polymethylene oxide, and polypropylene oxide;polyarylene oxides; polyesters, including polyarylates such aspolyethylene teraphthalate, polyimides, and other thermoplasticderivatives that are preferably solid at room temperature. Alternativelya tackifier or liquid adhesive could be used in addition to or insteadof a binder.

In another embodiment the solid contactor element may also be formedwith other useful constituents included in the element. Examples ofthese include, but are not limited to activated carbons and aluminas,which may be added to act to remove additional pollutants; fiberglass,carbon, and other fibers to reinforce the structure; silica gel; andmetallic particles such as iron, stainless steel, copper, aluminum, forexample. Other examples include ion-exchange resin, ceramics, zeolites,diatomaceous earth, particles of resins and plastics such aspolycarbonate, and non-thermoplastic polymer particles and fibers.

During the formation of solid contactor elements of the various typesdescribed, the compactor system may optionally include a means to mixthe material to be compacted, a preheater or precooler to control thetemperature of the material being fed to the compactor, heaters and/orcoolers along the extrusion die or within the mold to control thetemperature of the material as it is being compacted. Exemplarycompactor systems may also include a bin to store the material that isto be fed into the feed screw or mold, and/or a feed auger to forcematerial from the bin into the compactor feed screw or mold. Theseexemplary elements apply to the exemplary extrusion type compactor andthe mold press compactor described above and should not be construed tolimit the type of compactor employed in practicing methods of thisinvention to a certain type of compactor or to a compactor with certainelements.

In yet another embodiment of the invention, the metal oxides formed asdescribed herein may be used to remove metals and other contaminantsfrom aqueous streams or solutions such as drinking water supplies orprocessing streams. This invention relates in part to removal of metalsfrom aqueous solutions using oxides of manganese or other metal oxidesprepared according to the methods of the invention, e.g., oxides ofiron, titanium, or aluminum to name but a few. These solutions may bedrinking water supplies, industrial process or waste streams, or anyaqueous medium where pollutant removal is desired. The sorbentsynthesized or regenerated can be used as the removal medium by itself,it may be precipitated onto and/or within an inert substrate or anotheractive sorbent substrate such as activated carbons or activatedaluminas, it may be precipitated on a different metal oxide, or it maybe co-precipitated with one or more different metal oxides. This allowsexploitation of desirable sorbent particle characteristics such assurface area, pore size and volume, oxidation strength, and also allowsthe use of foreign metal cations which are either bound within the metaloxide structure or co-precipitated as a secondary oxide or as asubstrate to enhance certain characteristics of the metal oxides whenused in aqueous filtration systems. These beneficial characteristicslead to increased oxidation potential, amongst many othercharacteristics, for the metal oxides used in industrial and chemicalapplications. This includes the capture and removal of targetpollutants, such as arsenic, lead, copper, chromium, to name but a few,in aqueous filtration systems utilizing metal oxides of embodiments ofthe invention as a sorbent. The precipitation of the sorbent onto andwithin another active sorbent also allows for the simultaneous removalof metals, for example by an oxides of manganese sorbent, and organicpollutants, for example by an activated carbon substrate.

Other embodiments of the invention and the methods and systems thereofprovide for precipitation of highly active metal oxides such as oxidesof iron and oxides of magnesium, for example, onto and/or within inertor active sorbent substrates. The precipitation of oxides of manganeseonto and within another active sorbent granule, for example activatedcarbons or activated aluminas, allows for the simultaneous removal ofmetals that are removed by the metal oxides and organics that areremoved by the activated carbon, for example.

In yet other embodiments of the invention, metal oxides are formed intoan active solid contactor element that may be installed as a unit in andaqueous filtration system. This solid contactor element may be formed bycompacting the sorbent itself into a filter element, compacting thesorbent with other active sorbents into a solid contactor element, orcompacting the sorbent with a binder or tackifier material, possiblyalso with the inclusion of other active sorbents or reinforcingmaterials, for example.

With respect to the target pollutant arsenic, arsenic is found in waterin two common forms or species, arsenite (As⁺³) and arsenate (As⁺⁵).Arsenite is the most difficult to remove in conventional systems, and afeature of the sorbent of the present invention is that its highoxidation capability converts arsenite to arsenate which is more easilyremoved from the water. This oxidation capability of the sorbent isuseful in removing many metals from aqueous streams, arsenic being onlyexemplary. There are several technologies that can be used to achievethe new maximum contaminant level (MCL) for drinking water but many areeffective for removal of only one of the arsenic species. With the useof sorbent formed according to the methods of the invention, Applicantshave been able to effectively remove both of the two common arsenicspecies. Applicants have achieved arsenate and arsenite removal rates inexcess of 95% for both species with sorbents prepared according toembodiments of the methods of the invention. Exemplary removal rates foriron-based and manganese-based sorbents produced in accordance withembodiments of the invention are displayed in Table 1.

TABLE 1 Sorbent Arsenic Species % Removal Iron-Based As (+3) >98.6% As(+5) >98.4% Manganese-Based As (+3) >95.5% As (+5) >98.4%

In addition to removing both arsenic species and at higher removal ratesthan conventionally achieved, the processes of the invention havecreated sorbents that have the demonstrated ability to remove arsenicand hardness minerals to a level heretofore unachieved.

The metal oxides may be contacted with the metal or pollutant containingaqueous stream or medium in a number of fashions. For example the metaloxides particles can be fluidized or suspended in the aqueous mediumwithin a continuous reactor. Such a reactor could be a vertical vesselwith an inlet at the bottom for the metal containing water. The inletcould be configured so that the water enters the vessel at ahigh-velocity through a diffuser that creates a turbulent zone in thebottom region of the vessel. Metal oxides may be added to the vessel asa particulate powder but are preferably added as a slurry near thebottom of the vessel. The turbulence created by the aqueous streamentering through the diffuser suspends at least some of the metal oxidesin the solution. The suspended metal oxides may create a fluidized bedin the lower portion of the vessel.

A clear water overflow could be located sufficiently high on the vesselsuch that the suspended metal oxides have disengaged from the water flowand clear water can overflow substantially free of entrained metaloxides. This is easily accomplished by optimizing the diffuser design,the cross-sectional area of the vessel, and the sorbent particle size asdescribed above such that the velocity in the upper portion of thevessel is low enough that the metal oxides do not remain entrained. Theso-called clear water overflow may have sorbent that carries over andthat is then removed from the water stream by any solid-liquidseparation technology known in the art.

Fresh sorbent can continuously be added to the vessel as just described,and reacted sorbents can continuously be removed from the vessel throughan outlet located low enough in the vessel as to be in the fluidized bedportion. This stream may be continuous or intermittent and the oxides ofmanganese or other metal oxides and water may be further processedthrough filtration, centrifuging or other conventional solids/liquidsseparation process. The spent sorbent can be regenerated as describedabove. The system here is described as having one vessel, but therecould be any number of vessels involved, in series or in parallel. Asecond vessel in series is an effective way of ensuring adequatedisengagement of the metal oxides from the treated stream, for example.

The removal system could have a once-through flow of water with thewater stream entering through the diffuser, contacting the sorbent, andleaving the vessel as a treated stream. The system could also beconfigured with a recycle loop so that water is taken from the vessel ata point above the zone containing the suspended sorbent and recycledthrough the diffuser. This recycle loop could also take water from thezone with the suspended sorbent since, aside from erosion impacts onequipment such as the pump and diffuser, it is not important that therecycle stream be essentially free of sorbent. This recycle stream couldbe useful in controlling the water velocity in the vessel duringfluctuations in flow of the water stream to be treated. The recycleallows the operator to control the velocity of the water entering thevessel such that the velocity is high enough to suspend the sorbent andallow for sufficient contact of the sorbent with the target pollutantsand low enough that there is not excessive carryover of sorbent with thetreated stream.

While continuous reactors as just described may be used with theinvention, it is also possible to batch treat water by adding the waterto be treated and the sorbent to a vessel. The contents of the vesselcan be agitated or stirred to provide adequate contact between thesorbent and the target pollutants in the aqueous. After a sufficientreaction time the treated water may be separated from the particulatesorbent by decanting, filtering, microfiltration, centrifuging, or byother solid/liquid separation means known in the art.

For some applications, the sorbent may be precipitated onto filters orother structures. Further, the sorbent may be provided in pellet orother forms much larger than fine powders or particulates. The sorbentmaybe employed in a fluidized bed much like sand beds used in currentwater filtration plants. Systems that incorporate filters or thosesystems that do not have filters can be retrofitted to incorporatesorbent imbedded within a filter fabric or within a canister typefilter. Filtering systems may be multiple stages such as carbon followedby sorbent to allow for multiple pollutants to be removed. This is ofparticular advantage for home point-of-use devices such as faucetattachments or shower attachments. Another application would be portablewater bottle filters. These may also be multiple-stage filtration. Forexample, water maybe passed through a carbon stage followed by a sorbentstage and then a membrane type stage for filtration of microbialbacteria such as cryptosporidium or giardia. Sorbent may also beinjected into the filtration pipe and allowed to contact pollutantswithin the water stream and then subsequently be filtered out andregenerated. Thus, sorbents formed by the processes of the invention maybe utilized in a variety of commercial, industrial and residentialapplications in filtration systems known to those skilled in the art.Sorbent may also be formed into a solid contactor element comprisedentirely of sorbent creating a heretofore unavailable product.Alternatively sorbent may be formed into a composite solid contactorelement comprising one or more sorbents, a sorbent with a bindermaterial, sorbent with a reinforcing structural material, or anycombination of these elements and/or others described below. An exampleof a solid contactor element is a replaceable cartridge in a filterhousing. A solid contactor element may be conceivably of any size, fromseveral feet in diameter for industrial applications, to a size usefulin a personal water bottle, to an even smaller size useful in laboratoryequipment, for example.

In addition to such liquid-solid contactors as fluidized beds and batchvessels, the invention may also use fixed bed systems to remove targetpollutants from water. Such a fixed bed system is well known in the art,and usually includes a vessel, a bed of the sorbent within the vessel,and a means of support for the sorbent bed. The water to be treatedenters the vessel, passes through the bed where target pollutants arecaptured by the sorbent, and emerges from the vessel as a treatedstream.

Fixed bed contactors often include, depending on the target pollutantsto be removed, several different beds of sorbent or filter media. Such acontactor is referred to as a multi-media filter, even though chemicalreactions, absorption, adsorption, and other interactions as well asphysical filtration may be occurring. There may be, for example, a bedof ordinary sand as the first bed contacted by the water for removal byfiltration of suspended solids. There may also be a bed or beds ofactivated carbon, activated alumina, or other media useful in removingunwanted constituents from an aqueous stream.

Fixed bed contactors may also employ sorbent material with a largernominal size than the sorbent itself. This can be accomplished byforming solid contactor elements through compaction as disclosed aboveand loading several of them into a vessel to form a bed. As an exampleonly, extrudate cylinders approximately 5/16″ in diameter and ⅝″ longcould be formed by the compaction process previously described andloaded into a vessel to provide an easy to handle material which resultsin low overall pressure drop through the vessel due to the void spacescreated by the larger particle size. Particles of this size andconfiguration may be “random loaded” where they are simply dumped intothe vessel. When loaded in this configuration, they have a lower bulkdensity and associated pressure drop for a particular flow rate. Theseparticles may also be “dense loaded” in a process where they are loadedinto the vessel by means of a rotary spreader similar to those used inresidential lawn fertilization. When a vessel is dense loaded thepressure drop increases, but more sorbent may be added to a vessel of afixed size. Commercial operators of treatment systems may initiallydesign the system for a random loaded operation and, if the need formore capacity should arise in the future, may dense load the vessel andupgrade pumps to expand the capacity of the system without the need foran investment in another vessel.

Sorbent of this larger nominal size may also be created by precipitatingoxides of manganese or co-precipitating oxides of manganese with foreignmetal cations onto substrates of the desired size and shape. The sameprecipitation or co-precipitation process may be used with other metaloxides such as oxides of iron. Activated aluminas and activated carbons,for example, are commercially available in a wide variety of sizes andshapes. These active substrates, as well as other active and inactivesubstrates, may be used to create the physical configuration of sorbentparticle desired for the particular application.

Systems of fixed bed contactors may include more than one contactor, sothat while water is being treated by one contactor another is beingregenerated and prepared for reuse. This system may be arranged withcommon piping for a smooth on-line transition between vessels withoutinterruption of the flow of the stream to be treated. This type ofsystem may be configured such that when treating water, the water entersthrough the top of the vessel, and when regenerating the bed or beds,the regeneration fluid enters through the bottom. In this way theregeneration step also serves to “fluff” the bed or beds to reducecompaction caused during the treating process and to thus lower pressuredrop through the bed.

The regeneration of a bed of sorbent may be done in situ in the fashiondescribed above. That is a bed may be taken off-line, the loaded metaloxides can be rinsed while in the vessel, an ambient or heated aqueousoxidizing solution may be passed through the vessel, the solution beingprepared so as to have Eh and pH values within the metal oxide stabilityarea and with the heated oxidizing solution being monitored and adjustedso that solution temperature, Eh value and pH value are maintainedwithin the metal oxide stability area until the metal oxides areregenerated so as to reestablish pollutant loading capacity and/oraverage oxidation states to an acceptable level. The filtrate dependingupon the metal oxide used may now have the pollutant that was strippedfrom the metal oxide in a concentrated form. The oxidant, as an example,but not limited to, maybe hydrogen peroxide. This filtrate may now berouted to another vessel where ferric chloride or ferrous sulfate may beintroduced to capture the pollutant and bind it for disposal. Thisprocess is advantageous as the pollutant is concentrated along withother suspended particles when the bed is regenerated and smalleramounts of the binding agent are used. This leaves the sorbent in situand allows for repeated regenerations. Also, the oxidant breaks downinto water and is not hazardous to drinking water. After this iscomplete the bed may be put back on-line when another bed is spent andthe other bed can then be taken off-line and regenerated in the samemanner. Alternatively, the metal oxide sorbent may be removed from thecontact vessel and routed for regeneration as previously detailedhereinabove, utilizing either a batch or continuous flow reactor.

The use of foreign metal cations may provide for an increasedutilization of the sorbent for target pollutant removal. Increasedutilization can be achieved by selecting which foreign metal cation orcations to use and/or increasing the amounts of the particular metalcations used within the metal oxide structure. Foreign metal cations canincrease the reactive properties of the sorbent which are directlyrelated to capturing targeted pollutants or sorbent utilization.Applicants have found that by inserting specific foreign metal cations,such as titanium, into the metal oxide structure, the relative affinityfor various pollutants may be modified. Thus, sorbent can be selectivelyengineered to increase its utilization or affinity for differentpollutants, and may be selectively engineered to decrease its affinityor utilization for different pollutants. This will allow users to reducethe affinity for a benign component of the water stream while maximizingaffinity for target pollutants. For example if the water to be treatedhas a high iron content, sorbent may be modified to reduce its affinityfor iron relative to its affinity for arsenic if iron removal is not agoal of the system. This makes for a more cost efficient pollutioncontrol system as depending upon what pollutants are to be captured. Thepollutant with the lowest utilization will be the controlling factor indetermining how much sorbent is used in the system. This will affectcomponent sizing, thus reducing capital, and O & M costs. Selectiveengineering may also be advantageously utilized in dual-stage ormulti-stage removal systems where different pollutants are to beserially removed in different reaction zones.

The systems just described may be designed and sized to remove metalsfrom drinking water at a municipal water plant or at a single residence.They may also be configured for use in industrial processing, wastewatertreating, and any conceivable application for the claimed technology.

Yet another embodiment of the invention includes using the metal oxidesin a personal protective respirator to remove pollutants and/or toxinsfrom an air stream. The most common respirator is the half-maskrespirator. Half-mask respirators may be either disposable or reusable.Disposable half-mask respirators guard against either particulates,gases and vapors, or both. The half-mask respirator for gases and vaporsis disposed of when its filtering element is exhausted. This may occurwhen a user begins to smell or taste the chemical. Reusable half-masksrely on cartridges, some of which block out gases and vapors whileothers filter out particulates. The two types of cartridges are oftenused in tandem.

A variation on the reusable half-mask is the full mask, which protectsthe eyes and more of the face from splashes and flying particles thandoes the half-mask. Full masks also fit more snugly, minimizing thechance of leakage.

The full mask respirator includes a facepiece and a filter cartridge,sometimes also known as a “canister.” Straps are used to secure thefacepiece to a user's head. The cartridge may have a filter to removeparticles, a sorbent material to remove certain chemicals, both, orother parts. When the user inhales, air is pulled through the filter.Full mask respirators may also be of the positive pressure type withfiltered air being pressurized into the mask.

Advantages of respirators that remove airborne chemicals, also known asair-purifying respirators, are that they are less expensive and lesscomplicated than other options.

In a typical disposable filter respirator, a user's inhalation causesair to flow through the inlet, through a particulate filter, through afilter that includes a bed of particulate sorbent, through anotherparticulate filter (to trap sorbent dust) and through the outlet intothe mask. When the particulate filter clogs or the sorbent becomessaturated, you must replace the cartridge.

Chemicals in the form of mists or vapors are largely immune toparticulate filtration. The most common approach for removing an organicchemical is activated charcoal. Activated charcoals are widely used toadsorb odorous or colored substances from gases or liquids. The largesurface area of activated charcoal gives it many bonding sites to whichcertain chemicals may attach and be trapped. An activated-charcoalfilter will remove certain impurities while ignoring others.

Applicants have found that using the metal oxides of the invention,including metal oxides alone, co-precipitated metal oxides, metal oxidesincorporating foreign cations, metal oxides precipitated onto or with asubstrate such as, but not limited to, activated carbon, in a personalprotective respirator cartridge creates a respirator capable of removinga wide variety of pollutants in a safe manner. Applicants furtherbelieve that such respirator cartridges will last much longer thanconventional counterparts due to the high pollutant loading capacity ofthe sorbents of this invention.

In another embodiment of the invention, the metal oxides produced byembodiments of the invention are used in gaseous pollutant removalsystems. The following example describes such a pollutant removal systemintegrated with a metal oxide production system. In this example, oxidesof manganese are used to recover NO_(X) and SO_(X) from flue gases, itbeing understood that other this and other metal oxides may be used torecover these and other pollutants.

Turning to FIG. 8, the system 60 is a representation of pollutantremoval systems in general and it should be understood that the system60 could be a wet scrubbing removal system, a dry removal system or acombination thereof. System 60 as represented includes a reactionchamber 62 and a sorbent feeder 64 which contains and/or is configuredto feed oxides of manganese to the reaction chamber 62. Depending uponthe type of reaction chamber, oxides of manganese may be fed as a drypowder or dry particles, as slurry, or as a wet filter cake. Viewed as arepresentation of a Pahlman Process™ removal system, a stream ofuntreated gas containing target pollutants is shown entering into thereaction chamber 62. In this system 60, gas and sorbent oxides ofmanganese are introduced into the reaction chamber 62 and contactedunder conditions and for a time sufficient to effect removal of thetarget pollutant(s) at a targeted removal efficiency rate for the targetpollutant(s). It should be understood that the gas and the oxides ofmanganese may be introduced together or separately into reaction chamber62, depending upon the type pollutant removal system and type ofreaction chamber employed. Clean gas, gas from which a target pollutanthas been removed, is shown to be vented from the reaction chamber 62.Loaded oxides of manganese will be removed from the reaction chamber, asdry reacted sorbent, a filter cake of reacted sorbent or a slurry ofreacted sorbent and conveyed for regeneration and/or precipitationprocessing according to the invention with appropriate handling.

Described in greater detail, one of various embodiments of the PahlmanProcess™ system may be viewed as being comprised of a feeder containinga supply of sorbent or oxides of manganese, at least one bag houseconfigured to receive sorbent and a gas containing target pollutants,such as those identified herein above. Gas is introduced at temperaturesranging from ambient temperature to below the thermal decomposition orliquification temperature of manganese salt reaction products formedbetween the oxides of manganese and the target pollutant. Gases areintroduced into the bag house and contacted with the sorbent for a timesufficient to effect capture of the target pollutant at a targetedpollutant capture rate. The target pollutant or pollutants are capturedthrough formation of the reaction product between the target pollutantand the sorbent. The system will also include a controller forsimultaneously monitoring and adjusting system operational parameters.The controller provides integrated control of system differentialpressure and other operational parameters selected from the including,but not limited to, target pollutant capture rates, gas inlettemperatures, sorbent feeder rates and any combinations thereof. Thecontroller regulates differential pressure within the system so that anydifferential pressure across the system is no greater than apredetermined level and the target pollutant is removed at the targetedpollutant capture rate set point.

The system may incorporate more than one reaction zone, both of whichmay be bag houses. Alternatively, the system may optionally incorporatea reaction zone upstream of a bag house into which gas and sorbent areintroduced and subsequently directed to the bag house. Such optionalreaction zones may be selected from the group of reaction zones thatincludes a bag house, fluidized bed, a pseudo-fluidized bed, a reactioncolumn, a fixed bed, a moving bed, a serpentine reactor, a section ofpipe or duct, an absorber, and a cyclone or multi-clone. When tworeaction zones are thus connected and the gas stream contains at leasttwo target pollutants, such as SO_(x) and NO_(x), for example, the firsttarget pollutant may be captured or removed in the first reaction zoneor substantially removed in the first reaction zone and the secondtarget pollutant will be removed in the second reaction zone. This canbe advantageously utilized particularly where the two reaction zones arebag houses to capture a first target pollutant such as SO_(x) in thefirst reaction zone and a second target pollutant such as NO_(x) ormercury in the second reaction zone. This would allow for separateregeneration of loaded sorbent having reaction products thereon fromreaction between oxides of manganese and a single target pollutant or atleast different target pollutants that are captured in the second baghouse. Thus, if the target pollutants are SO_(x) and NO this would allowfor separate regeneration and filtration of a SO_(x) loaded sorbent andNO sorbent with their respective reaction product ions beingdisassociated into separate pre-oxidation rinses with the resultantpre-oxidation filtrates also being separately processed to precipitateout oxides of manganese. The respective precipitation filtrates wouldthen allow for separate production of sulfate by-products and nitrateby-products.

The system may also include three or more reaction chambers 62 connectedto a common conduit with one or more diverter valve(s) positioned in thecommon conduit to direct the flow of gas to the first reaction chamber62, to the second reaction chamber 62 and/or the third reaction chamber62. The diverter valve(s) have variable positions that may includefirst, second and third positions, and so on in sequence. The conduit,diverter valve(s) and reaction chambers 62 are configured so that gasmay be routed through any one of the reaction chambers 62, any two ofthe reaction chambers 62 in series, or all of the at least threereaction chambers 62 in series or in parallel, or any combination ofseries and parallel.

With reference to FIG. 8, a regeneration system 10 and precipitationsystem 30 substantially as depicted in FIG. 3 is illustrated in blockflow and is connected to removal system 60. Continuous flow reactor 24is equipped with temperature probe 13A, pH probe 13B, and Eh probe 13C,and pressure probe 13D; continuous flow reactor 14 is equipped withtemperature probe 13A, pH probe 13B, Eh probe 13C, and pressure probe13D all of which are in electronic communication with a controller 67. Apremixed oxidant/base vessel (not shown) containing a preheatedoxidant/base solution is configured to feed said solution to continuousflow reactor 24 and continuous flow reactor 14. Alternatively, preheatedoxidant/base solution may be routed directly from an electrolytic cell72, such as shown in FIG. 11, or the output of electrolytic cell 72 maybe routed to the oxidant vessel. Loaded sorbent may conveyed directlyfrom reaction chamber 62 to regeneration pre-oxidation rinse 12 or itmay be directed to a loaded sorbent vessel (not shown) for holding andsubsequently conveyed to rinse device 12. The pre-oxidation filtratefrom rinse 12 is routed to the continuous flow reactor 24. The rinsedsorbent from pre-oxidation rinse device 12 is slurried as appropriateand routed to the continuous flow reactor 14.

The feeders (not shown) of the premixed oxidant/base vessel,oxidant/base/acid vessel, and loaded sorbent slurry vessels (not shown)are in electronic communication with the controller 67. The controller67 is also in electronic communication with the Eh probe 13C, pH probe13B, temperature probe 13A, and pressure probe 13D with which thecontinuous flow reactor 34 is equipped and Eh probe 13C, pH probe 13B,temperature probe 13A, and pressure probe 13D with which the continuousflow reactor 14 is equipped.

As illustrated, newly precipitated or virgin sorbent from the continuousflow reactor 24 and regenerated sorbent from the continuous flow reactor14 is routed to filtration unit 16 for filtering. The sorbent is furtherrouted to the rinse device 17 to be further rinsed. Alternatively,filtration unit 16 and rinse 17 may be combined into one device so as toremove filtrate and rinse in a combined operation. Also, sorbent fromthe continuous flow reactor 24 and the sorbent from continuous flowreactor 14 may each have its own filtration device and sorbent rinsedevice. Sorbent is then routed to the sorbent dryer 18 As illustrated,sorbent from sorbent dryer 18 is routed to comminuting device 19 andthen to sorbent feeder 64 which in turn feeds the sorbent to reactionchamber 62. Alternatively, sorbent from dryer 18 may be routed directlyto reaction chamber 62 or to a sorbent storage vessel prior to beingdirected to the feeder 64.

Reaction chamber 62 is equipped with optional target pollutantconcentration readers or continuous emission monitors (CEMS) for NO_(X)and SO₂, readers 68A and 68B, which are in electronic communication withcontroller 67. It should be understood the reaction chamber 62 may beequipped with other equivalent readers where different target pollutantsare being captured.

The controller 67 interfaces with continuous flow reactor 24 probes 13A,13B, 13C, and 13D; NO_(X) and SO₂ readers 68A and 68B and the premixedoxidant/base vessel, and oxidant/base/acid vessel feeders and vessels(not shown) for measurement and adjustment of operational parameterswithin reactor 14 and 24. The controller 67 signals the addition ofpremixed oxidant/base, oxidant, acid, and/or base to continuous flowreactor 24 based upon the inputs received from the probes until thedesired Eh/pH reading is obtained prior to addition of the pre-oxidationfiltrate into the continuous flow reactor 24. Or controller 67 can beprogrammed with initial set points corresponding to predeterminedamounts of chemical constituents to be added to process solutions basedupon historical process data that has been retained. The static mixer oragitator 35 continuously agitates and mixes the combined mixed thesolution as it travels through the pipe or continuous flow reactor. Thetemperature, pressure, pH, and Eh conditions in the continuous flowreactor 24 are monitored and adjusted continuously so as to maintainconditions within the MnO₂ stability area.

The controller 67 similarly interfaces with regeneration vessel 14probes 13A, 13B, 13C, and 13D; NO_(X) and SO₂ readers 68A and 68B andthe premixed oxidant/base vessel, and oxidant/base/acid vessel feedersand vessels (not shown) for measurement and adjustment of operationalparameters within the vessel 14. Thus, temperature, pressure pH, and Ehconditions in the regeneration slurry in continuous flow reactor 14 aremonitored and adjusted continuously so as to maintain conditions withinthe MnO₂ stability area. Continuous flow reactor 24 and continuous flowreactor 14 may be run in parallel operation or alternating operation soas to be able to verify sorbent loading capability using, an optionalfeedback loop of the controller 67 and probes 68A and 68B.

The controller 67 contains a programmable logic controller (PLC) andother hardware components necessary for the operation of the controllersuch as a power supply, input and output modules that would communicatewith the probes 13A, 13B, 13C, 13D of system 10; probes 13A, 13B, 13C,and 13D of system 30 and/or readers 68A and 68B, and with the premixedoxidant/base vessel, and oxidant/base/acid vessel feeders and vessels(not shown), and loaded sorbent feeder (not shown) and other components.The controller 67 receives inputs from the various probes and readersand converts them into ladder logic language that would be used by aninternal control loop, such as a proportional integral derivative (PID)loop or derivation thereof, to individually and simultaneously monitorsystem operational parameters and to reconcile the inputs withpredetermined or computer generated calculated set points for theoperational parameters, such as temperature, pressure, Eh, and pHlevels, sorbent loading and target pollutant removal or capture rate. Asdetermined by computer logic, the controller 67 will send an output asnecessary to any of the feeders of premixed oxidant/base vessel, andoxidant/base/acid vessel (not shown) signaling a feeder to cycle on orto change feeder rate so as to maintain or adjust system operationalparameters to within the MnO₂ stability area for either continuous flowreactor 24 or continuous flow reactor vessel 14. The controller 67 mayalso contain an Ethernet card or other component that allows onsite oroffsite remote display and operator interface and control as needed.

The controller 67 would be given a start command and direct the loadedsorbent feeder (not shown) to inject predetermined amounts of loadedsorbent into the pre-oxidation rinse device 12. The controller 67 wouldalso signal injection of a predetermined amount of premixed oxidant/basesolution to continuous flow reactor 24 and continuous flow reactor 14while checking and or adjusting the Eh and/or pH of the solution priorto simultaneously feeding in the predetermined amount of pre-oxidationfiltrate from the pre-oxidation rinse device 12 into continuous flowreactor 24 and a predetermined amount of rinsed sorbent slurry from thepre-oxidation rinse device 12 into continuous flow reactor 14. The Eh ofthe precipitation solution in continuous flow reactor 24 and of theregeneration slurry in continuous flow reactor 14 may further beadjusted by addition of an oxidizer in sufficient quantity as to raisethe Eh to the desired level from an oxidizer vessel (not shown),containing a supply of oxidizer or aqueous oxidizing solution.

As determined by programmed controller logic, the controller 67 wouldalso check, based on inputs received from precipitation reactor 24 andassociated probes 13A, 13B, 13C, and 13D; and continuous flowregeneration vessel 14 and associated probes 13A, 13B, 13C, and 13D.Controller 67 may also check TDS levels base upon inputs received froman optional TDS probe, if provided, for verification and adjustment ofmolar concentrations of process solution constituents as needed.Conditions in the precipitation solution and in the regeneration slurrymay further be adjusted by utilizing a heater or heat exchanger (notshown) to increase or decrease solution temperature; the pH, if needed,by increasing or decreasing the rate of base or acid feed; the Eh, ifneeded, by increasing or decreasing the oxidizer concentration of theaqueous oxidizing solution or oxidant/base pre-mixed solution; and thepressure, if needed, by controlling the backpressure valve 94

An optional, final quality control loop may be provided, as shown,utilizing the readers 68A and 68B to check the loading performance ofthe processed oxides of manganese sorbent by sending, for example,SO_(X) and NO_(X) readings back to the controller 67. As determined bycontroller logic, the controller 67 would then adjust continuous flowreactor 24 and/or continuous flow reactor 14 parameters, if needed, toprovide precipitated oxides of manganese and regenerated oxides ofmanganese, respectively, capable of removing target pollutants at thetargeted removal rates.

The same controller may also be used to control the entire operation ofthe removal system 60, the regeneration system 10 and the precipitationsystem 30 and their components as discussed above including,pre-oxidation rinse 12, filtration unit 16, rinse device 17, dryer 18,comminuting device 19, sorbent feeder device 64 and the by-productsprocessing vessel 66, and electrolytic cell device (not shown butdepicted in FIG. 11) or separate controllers may be provided fordifferent components or group of components or functions.

With reference to FIG. 9, the regeneration and precipitation system 10is depicted as integrated with removal system 60. In the interest ofavoiding undue repetition, Applicants note that the operation andcontrol of the integrated systems 10 and 60 with controller 67 can beunderstood as being substantially the same with respect to correspondingcomponents, shown and not shown, as described immediately above withrespect to the integrated systems 10, 30 and 60. The controller 67 willbe in electronic communication with the probes of a single continuousflow regeneration/precipitation reactor 14; otherwise, the operation andfunctions of electronic control and communication is substantially thesame as described. With reference to FIG. 10, this is equally applicableto the integration of systems 10 and 60 and the operation and functionof electronic communication and control of the corresponding systemcomponents. Note that a variation of regeneration and precipitationmethod is illustrated. In FIG. 10, reacted sorbent is rinsed andfiltered and routed to dryer 17. It is not directed to a continuous flowreactor but the pre-oxidation filtrate is routed to continuous flowreactor 14 where precipitation is carried out as previously described.This variation of the method of the invention can be used where theloading capacity oxides of manganese below the reaction product surfacecoating on the sorbent particles has not been so significantlydiminished during pollutant removal as to required chemicalregeneration. In such cases, it is sufficient to wash away the reactionproducts, dissolving and disassociating them into the rinse solution orpre-oxidation filtrate and the rinsed oxides of manganese can then bedried and comminuted if necessary prior to being reused to capturetarget pollutants. Applicants have found that where the gas streamcontains primarily concentrations of SO_(X) a regeneration rinse isoften all that is required prior to reuse of the rinsed sorbent, withrecovery of reaction product ions through precipitation and otherprocessing.

In yet another embodiment, the continuous pollutant removal process maybe operated with permanganate injection in order to provide additionalmeans of metals removal in a pollutant removal system such as thePahlman Process™ system. In such an embodiment, a slipstream is takenfrom the solution in the continuous flow reactor prior to the solutiongoing from the permanganate region of the Pourbaix equilibrium diagramand into the MnO₂ region and routed to a spray drying nozzle. Thepermanganate containing slipstream can be injected into the pollutantremoval system or upstream thereof and contacted with the targetpollutant containing gas and entrained sorbent. Where after start up,the sorbent is being provided by one or more MnO₂ injection spray, theslip stream and MnO₂ may be injected at different stages from multiplenozzles or multiple injection points either separately orsimultaneously, with the injections sequenced or coordinated, asnecessary, to provide optimal utilization of the permanganates formetals removal. The permanganate may be injected in varyingconcentrations, as necessary, depending upon concentrations of mercury(elemental, oxidized or total mercury compounds) or other heavy metalcompound in the gas stream. This will assist in converting metals fromelemental or other reduced states into oxidized metals and lead furtherto capturing the oxidized mercury or other oxidized metals in a baghousereactor, such as in a Pahlman Process™ pollutant removal system. Theprocess of capturing mercury or other heavy metals may or may not dependupon oxidizing them with permanganate; and the capture of some but notnecessarily all such pollutants may be aided by a permanganateinjection. If metal oxides other than oxides of manganese are used assorbents, potassium permanganate may be purchased and injected from aseparate tank outside the system rather than use the slipstream of theMnO₂ continuous process. The tank concentration may be varied asrequired to maintain capture rates of mercury as necessary.

The permanganate, after capture in the baghouse and going through theregeneration process, will convert to a lower oxide of manganese as itis water soluble and stay within the system. This will create a closedloop process where none of the manganese is lost no matter what form itmay be in. The metal oxide filter cake leaving filter press may berouted for further handling and processing such as drying andcomminuting prior to introduction into a sorbent feeder and subsequentlyfeed into or upstream of a baghouse reactor. Or the filter cake beconveyed to a filter cake feeder or mixed into a slurry and routed to aspray dryer or nozzles prior to the baghouse reactor.

Applicants have prepared specific illustrative examples which arediscussed and summarized in the following discussion.

One on the key aspects of the various embodiments of the Applicants'invention is the ability to control specific metal oxide particlecharacteristics such as: particle surface area, bulk density, pore size,pore volume and other characteristics like particle density andnanofiber dimensions. These metal oxide characteristics affect thesorbent's ability to affect target pollutants thus affecting utilizationand cost of the process. Large values for particle surface area meansthere are more potential reaction sites at the surface of the sorbent,so less particles need to migrate into the structure to be captured.Pores volume and size regulate how readily diffusion of mobile specieslike cations occurs. Pore volume and size are controlled with theaddition of foreign cations. The cations can modify the latticestructure by increasing lattice defects during the nanofiber growthprocess. For example, this affect can lead to larger pore volumes and/ormore pores with smaller volumes depending on how the structures stacktogether. These properties ultimately affect sorbent/pollutant reactionkinetics and utilization; therefore, to be able to manipulate theseparameters is important. Bulk density is important for transportationpurposes; for example, the sorbent needs to have a low bulk density soit can be adequately mixed by the flue gas to initiate reaction. All ofthese particle characteristics can be affected or controlled through theembodiments of the Applicants' invention by introducing metal cations ofprimary and secondary metal into metal oxides or metal oxide compoundsand by precipitating the various metal oxides onto substrates.

Example 1

As an illustrative example not intended to be limiting in scope, metaloxide based sorbents created with foreign cation addition techniques andmetal precipitation onto substrates as detailed in the Applicant'sinvention using either the continuous flow reactor or batch processesare detailed in the following example. A series of metal oxide basedsorbents were created and analyzed for specific particlecharacteristics. Table 2, provides a summary of the prepared metal oxidesorbents along with a summary of key particle characteristic data.

Eleven metal oxide sorbents were all produced in accordance to themethods of the Applicant's invention and utilized potassium persulfate(K₂S₂O₈) as the oxidant in the oxidizing aqueous solution and potassiumhydroxide (KOH) and for pH control and are all labeled A-K in Table 2.Seven of the sorbents, labeled A-G, were prepared utilizing theApplicant's inventive concept of adding metal cations of primary andsecondary metals to a newly precipitated metal oxide, in this case MnO₂.As to not be redundant and repetitive, metal oxide sorbent A will bedescribed in detail, and it should be understood that all seven (A-G)were prepared in the same manner except for the addition of a differentsoluble metal salt. Turning now to sorbent A, a metal oxide soluble saltsolution of 1/16 Mole BaSO₄ was added to 1.0 Mole solution of MnSO₄.Upon contacting the oxidizing aqueous solution and combined solublemetal salt solution, process parameters were controlled and maintainedaccording to the methods of the Applicant's invention with respect tosystem temperature, pressure, Eh, and pH and controlled with respect tothe systems metal oxide stability area. Sorbent A is thus composed of aprimary metal oxide MnO₂ with incorporation of a primary metal cation,namely Ba⁺² and a secondary metal cation, namely K⁺². The K⁺²originating from the potassium persulfate (K₂S₂O₈) used to prepare theoxidizing aqueous solution and base (KOH) addition for pH control duringprocessing. The remaining 6 sorbents B-G were prepared identically, withthe exception of the soluble metal salt namely: Li₂SO₄, CuSO₄, MgSO₄,Al₂(SO₄)₃, Ti₂(SO₄)₃ and Fe₂(SO₄)₃. From looking at the particleanalysis data in Table 2, it can be seen that through the addition ofselected primary and secondary metal cations to the precipitated primarymetal oxide, in this case MnO₂, important particle physical propertiessuch as particle size, surface area, and bulk density can be controlledto optimize the sorbents target pollutant removal rates.

For four of the eleven metal oxide sorbents, labeled H-K as illustratedin Table 2, the practice of precipitating metal oxides onto insolublesubstrates was demonstrated as outlined in the Applicants' invention.Sorbents H-K all started with 1.0 Mole of a soluble metal salt which wasintended to be the primary metal oxide precipitate, in this casemanganese sulfate (MnSO₄), and to that soluble metal salt solution ¼Mole of one of the following substrates was respectively added: forsample “H”, iron (III) oxide (Fe₂O₃), for sample “I”, magnesium (II)Oxide (MgO) for sample “J” and titanium (IV) oxide (TiO₂), and forsample “K” aluminum (III) oxide (Al₂O₃). For metal oxide sorbents H-Kthe oxidizing aqueous solution and base addition for pH control wasagain potassium persulfate and KOH. It should therefore be noted thatthe primary metal oxide being precipitated on the various substrates wasMnO₂, however, incorporation of a foreign cation, namely K⁺² was alsotaking place. Referring again to the particle analysis data in Table 2,it can be seen that the Applicants' method of precipitating a primarymetal oxide onto an insoluble substrate along with the addition ofselected foreign cations (K⁺²) to the primary precipitated metal oxide,in this case MnO₂, important particle physical properties such asparticle size, surface area, and bulk density can be engineered orcontrolled to optimize the sorbents target pollutant removal rates. Forcomparative purposes, a sorbent labeled as “baseline” is provided. Thebaseline sorbent was produced according to the methods of the inventionwith a 1.0 Mole solution of MnSO₄ and potassium persulfate supplied inthe aqueous oxidizing solution and potassium hydroxide for Ph control.

TABLE 2 Metal Oxide Particle Data Bulk Foreign Surface Area ParticleSize Density Sample ID Cation Substrate (m²/g) (microns) (g/cc) BaselineK 263 12.1 0.520 Foreign Cation Addition A Ba 157 12.4 0.434 B Li 24613.4 0.447 C Cu 286 11.9 0.553 D Mg 318 11.6 0.445 E Al 330 13.2 0.338 FTi 378 11.1 0.414 G Fe(III) 445 12.8 0.408 Substrate Precipitation HFe₂O₃ 227 5.5 0.552 I MgO 314 22.1 0.359 J TiO₂ 315 12.8 0.463 K Al₂O₃365 15.9 0.473

Example 2

As an illustrative example, metal oxide based sorbents created withforeign cation addition techniques and metal precipitation ontosubstrates as detailed in the Applicant's invention using either thecontinuous flow reactor or batch processes are detailed in this Example2. In Example 2, a series of metal oxide based sorbents were created andtested for removal of various target pollutants. Table 3, provides asummary of the prepared metal oxide sorbents and target pollutantremoval data.

The metal oxide sorbents 1-6 were all precipitated in accordance to themethods of the Applicant's invention and utilized potassium persulfate(K₂S₂O₈) and potassium hydroxide (KOH) and the oxidizing aqueoussolution. Sorbent 1 was prepared utilizing the Applicant's inventiveconcept of adding a primary and secondary metal cation to a newlyprecipitated metal oxide, in the case Fe₂O₃. For Sorbent 1, a metaloxide soluble salt solution of 0.5 Mole Fe₂(SO₄)₃ and 1/32 mole MnSO₄was prepared. Upon contacting the oxidizing aqueous solution and solublemetal salt solution, process parameters were controlled and maintainedaccording to the methods of the Applicant's invention with respect tosystem temperature, pressure, Eh, and pH and controlled with respect tothe systems metal oxide stability area. Sorbent 1 contains a primarymetal oxide Fe₂O₃ with incorporation of a primary metal cation, namelyMn⁺² and a secondary metal cation, namely K⁺², from the oxidant and baseinto the crystalline structure. Sorbent 2 was prepared in the samemanner as Sorbent 1, however, the soluble metal salt solution containedonly 0.5 Mole of Fe₂(SO₄)₃. Therefore, Sorbent 2 was composed of aprimary metal oxide Fe₂O₃ with incorporation of a foreign cation, namelyK⁺², from the oxidant and base oxidizing aqueous solution and baseaddition for pH control during processing. Again, Sorbent 3 was preparedin the same manner as Sorbent 1, however, the soluble metal saltsolution contained only 1.0 mole of manganese sulfate (MnSO₄). Sorbent3, therefore, was composed of a primary metal oxide MnO₂ withincorporation of a foreign cation, namely K⁺², from the oxidant and baseoxidizing aqueous solution and base addition for pH control duringprocessing. As an illustrative example not intended to be limiting, the% potassium incorporated into the MnO₂ structure of Sorbent 3 wasmeasured through compositional analysis to be 6.81% by weight with 18%structural water. As the compositional analysis indicates, it should benoted that the sorbent represented as MnO₂ can alternatively berepresented as K_(y)MnO_(x)*zH₂O. Other metal oxides and metal oxidecompounds incorporate foreign cations prepared by methods of theinvention may be similarly analyzed and represented.

Sorbents 4-6 were prepared by utilizing the method in the Applicant'sinvention of precipitating metal oxides onto insoluble substrates.Sorbents 4-6 all started with a soluble metal salt, specificallymanganese sulfate (MnSO₄), and added ⅛ Mole quantities, respectively, ofiron (III) oxide (Fe₂O₃), aluminum (III) oxide (Al₂O₃), and titanium(IV) oxide (TiO₂) to the starting soluble metal salt solution. Sorbent 4contained the (Fe₂O₃), Sorbent 5 contained (Al₂O₃), and sorbent 6contained (TiO₂). For Sorbents 4-6 the oxidizing aqueous solution andbase addition for pH control was again potassium persulfate and KOH. Itshould therefore be noted that the primary metal oxide beingprecipitated on the various substrates was MnO₂, however, incorporationof a primary foreign cation, namely K⁺².

Each of the six sorbents were tested for their ability to remove atarget pollutant from water, in this case the two common forms ofarsenic. Known concentrations of arsenite (As⁺³) and arsenate (As⁺⁵)were both spiked in an aliquot of typical drinking water. A knownquantity of sorbent was then mixed with the contaminated aliquot andfiltered. After filtering, the effluent water was tested for thepresence of the contaminating arsenic ion using the induced coupledplasma (ICP) analytical technique. Removal percentages were thencalculated and are presented in Table 2. In all cases, the metal oxidesorbent removed both forms of arsenic down to the detection limit of theanalysis method.

The removal of water hardness, as represented by concentrations ofcalcium (Ca) and/or magnesium (Mg) ions present in the water samples,was also conducted on samples of Sorbents 1-3. Similar to the arsenictesting procedure, drinking water aliquots were spiked with knownconcentrations of Ca and Mg, mixed with a specified amount of sorbent,separated through filtration and the resulting liquid was tested for thepresence of either cation. Cation detection was determined usingstandard titration analytical procedure. Removal percentages were thancalculated and presented in Table 3. The degree of water hardnessremoval can be seen to vary for metal oxide sorbents produced by thedifferent embodiments of the Applicant's invention.

Each sorbent removed both forms of arsenic to concentrations below thedetection limits of the analytical equipment used. However, the degreeof water hardness removal could be varied based upon both the type ofmetal oxide sorbent produced and the addition of different foreigncations into the primary metal oxides crystalline structure.

TABLE 3 Solution Initial Final % Removal Sorbent 1: 0.5 Mole Fe₂(SO₄)₃and 1/32 mole MnSO₄ As[III] from As₂O₃ 0.69 mg/L <0.01 mg/L >98.6%  As[V] from AsHNa₂O₄ 0.61 mg/L <0.01 mg/L >98.4%   Ca Hardness (ppm) 200200    0% Mg Hardness (ppm) 160 160    0% Sorbent 2: 0.5 Mole Fe₂(SO₄)₃As[III] from As₂O₃ 0.26 mg/L <0.01 mg/L >96.2%   As[V] from AsHNa₂O₄0.61 mg/L <0.01 mg/L >98.4%   Ca Hardness (ppm) 200 155 22.50%   MgHardness (ppm) 160 140 12.50%   Sorbent 3: 1.0 Mole MnSO₄ As[III] fromAs₂O₃ 0.082 mg/L <0.04 mg/L >95% As[V] from AsHNa₂O₄ 0.096 mg/L <0.04mg/L >96% Ca Hardness (ppm) 200 50   75% Mg Hardness (ppm) 160 0 100%Sorbent 4: 1.0 Mole MnSO₄ and ⅛ Mole Fe₂O₃ Substrate As[III] from As₂O₃0.082 mg/L <0.04 mg/L >95% As[V] from AsHNa₂O₄ 0.096 mg/L <0.04mg/L >96% Sorbent 5: 1.0 Mole MnSO₄ and ⅛ Mole Al₂O₃ Substrate As[III]from As₂O₃ 0.082 mg/L <0.04 mg/L >95% As[V] from AsHNa₂O₄ 0.096 mg/L<0.04 mg/L >96% Sorbent 6: 1.0 Mole MnSO₄ and ⅛ Mole TiO₂ SubstrateAs[III] from As₂O₃ 0.082 mg/L <0.04 mg/L >95% As[V] from AsHNa₂O₄ 0.096mg/L <0.04 mg/L >96%

Examples 3-5

As discussed, the ability of metal oxide based sorbents to remove targetpollutants can be controlled through various embodiments of theApplicant's invention. One such embodiment is by introducing foreignmetal cations into the primary metal oxides crystalline structure. Theseforeign metal cations can be introduced in multiple ways during theprocesses as detailed previously in the multiple embodiments of theinvention, both in a batch or continuous flow reactor process. One suchmethod for the introduction involves the metal cations associated withthe specific oxidants and bases used to prepare the oxidizing aqueoussolution and base for pH control. By way of non-limiting example,potassium (K₂S₂O₈) and sodium (Na₂S₂O₈) persulfates and potassium (KOH)and sodium (NaOH) hydroxides can supply a K⁺² or Na⁺² to the primarymetal oxide. Foreign cation introduction can alternatively beaccomplished by using a soluble metal salt solution, such as K₂SO₄ orNaSO₄, as utilized when levels of K and Na desired in the metal oxideare beyond those that could be achieved by the quantities of cationspresent as result of oxidant and base additions. Additional cationscould alternatively be added, such as: Ba²⁺, Al³⁺, and Mg²⁺, by usingtheir soluble salt forms.

As previously noted, the precipitation should be carried out solely witha region of the primary metal oxide stability areas and not in aco-precipitation area of both the primary metal and the metal foreigncation, to avoid co-precipitation. If co-precipitation is desired, theprocessing should be carried within the co-precipitation stability area.

An additional embodiment of the Applicant's invention that allowscontrol of the metal oxides' target pollutant removal property would beintroducing various substrates into both the batch and continuousprocess. In the following example, manganese dioxide based sorbents werecreated according to methods of the invention and tested for theirtarget pollutant utilization using a flue gas stream from a coal-firedutility boiler facility. The target pollutant laden gas stream waspassed through a glass reactor containing several grams of a specifiedmetal oxide sorbent that was prepared consistent with the methodsoutlined previously. In this case, the target pollutants were NOx andSOx. Specific removal capabilities of various metal oxide sorbents areexpressed as the sorbents' utilization and calculated by taking moles ofpollutant removed during the test period to a specified breakthroughlevel (in this case 90% removal) and dividing by moles of sorbent usedin the reactor test (approximately 5.0 grams).

Example 3

Three metal oxide sorbents were prepared using the introduction of theforeign cations associated with the specific oxidant and base.Specifically, the ammonium (NH₄ ⁺) cation from ammonium persulfate andhydroxide, sodium (Na²⁺) cation from sodium persulfate and hydroxide andpotassium (K⁺) from potassium persulfate and hydroxide. Testing resultsindicate that the MnO₂ metal oxide sorbent with an ammonium (NH₄ ⁺)foreign cation bound into the crystalline structure has a NO_(x)utilization that is 1.9 times greater than an identical MnO₂ metal oxidesorbent prepared with sodium (Na²⁺) as the foreign cation bound into thecrystalline structure. Additionally, the MnO₂ sorbent prepared withpotassium (K⁺) as the foreign cation bound into the crystallinestructure exhibited NOx utilization 2.1 times greater than the MnO₂sorbent with sodium (Na²⁺) and 1.1 times greater than MnO₂ sorbent withammonium (NH₄ ⁺) as the foreign cation bound into the crystallinestructure.

Example 4

As an additional example, four manganese based metal oxide sorbents wereprepared using the introduction of both a first foreign metal cationassociated with the specific oxidant and base, in this case K, from thepotassium persulfate and potassium hydroxide and additionally a secondforeign metal cation introduced into the system through a soluble cationmetal salt. ¼ Mole of the soluble cation salt was added to a 1.0 Molesolution of manganese sulfate (MnSO₄) and the process as operated andcontrolled according to the Applicants' invention with respect totemperature, pressure, Eh, and pH and maintained in the desired metaloxide stability area. The aqueous oxidizing solution was composed of 1.4Moles of potassium persulfate (K₂S₂O₈) and potassium hydroxide was usedfor pH control. Specifically foreign cations added in the four samplesinclude: barium (Ba²⁺), iron (Fe³⁺), magnesium (Mg²⁺), and aluminum(Al³⁺). The four metal oxide sorbents were then tested for their targetpollutant removal and ranked according to their mass utilization.Testing was again carried out using a flue gas stream from a coal-firedutility boiler facility. A target pollutant laden flue gas stream waspassed through a glass reactor containing several grams of each of thefour metal oxide sorbents. In this case, the target pollutants were NOxand SOx. Specific removal capabilities of various metal oxide sorbentsare expressed as the sorbents' utilization and calculated by takingmoles of pollutant removed during the test period to a specifiedbreakthrough level (in this case 90% removal) and dividing by moles ofsorbent used in the reactor test (approximately 5.0 grams).

The manganese based metal oxide sorbent with barium (Ba²⁺) added as asecond foreign metal cation (K was the first foreign metal cation) had aSO_(X) utilization that was 2.2 times greater than the manganese basedmetal oxide sorbent with iron (Fe³⁺) added as the secondary foreignmetal cation. Additionally, manganese based metal oxide sorbent withaluminum (Al³⁺) added as a secondary foreign metal cation (K was theprimary foreign metal cation) had a NO_(x) utilization that was 1.6times greater than the manganese based metal oxide sorbent with aluminum(Al³⁺) added as a secondary foreign metal cation.

Example 5

In an additional example, two manganese based metal oxides wereprecipitated onto substrates of aluminum (Al₂O₃) and magnesium (MgO).Precipitation of the manganese based metal oxides onto a substrate wascarried out as specified above in the Applicants' invention. 1.0 Mole ofmanganese sulfate (MnSO₄) and ¼ Mole aluminum (Al₂O₃) for sample 1 and1.0 Mole of manganese sulfate (MnSO₄) and ¼ Mole magnesium (MgO) forsample 2 was treated with the aqueous oxidizing solution, in this casecomposed of K₂S₂O₈ with pH control being accomplished with KOH wasprocessed according to the invention as relating to control oftemperature, pressure, molarity, Eh, and pH and within the metal oxides'stability area. The two sorbents' mass utilization, where NO_(X) was thetarget pollutant were determined in similar fashion as the foreigncation metal oxide manganese based sorbent as described above. It wasfound that the manganese based metal oxide sorbent prepared on thealuminum (Al₂O₃) substrate had a NO_(x) utilization that was 1.2 timesgreater than the manganese based metal oxide sorbent prepared onmagnesium a (MgO) substrate.

Therefore, it can be illustrated that application of the methods of theApplicants' invention can be utilized to produce metal oxide sorbents,both with foreign metal cations and on substrates with varying degreesof target pollutant loading rates, as expressed as mass utilization.

While exemplary embodiments of this invention and methods of practicingthe same have been illustrated and described, it should be understoodthat various changes, adaptations, and modifications might be madetherein without departing from the spirit of the invention and the scopeof the appended claims.

1. A system for the removal of metals from an aqueous solutioncomprising a contactor adapted for contacting an aqueous solutioncontaining at least one target pollutant with a sorbent, wherein thesorbent removes at least a portion of said target pollutant from saidaqueous stream, said sorbent material comprising metal oxides formed bythe process of; a. mixing a metal containing solution and an aqueousoxidizing solution in a sorbent production reactor to form a solutionmixture, the heated aqueous oxidizing solution being prepared so as tohave Eh and pH values within a polyatomic ion stability area, metal ionstability area, a metal oxide stability area, or a co-precipitationstability area of an aqueous solution at process temperature and processpressure when the aqueous oxidizing solution is mixed with the metalcontaining solution; b. monitoring and adjusting the temperature, Ehvalue and pH value of the solution mixture so as to rapidly move mixtureconditions into and to maintain them within the metal oxide stabilityarea or co-precipitation stability area; and c. maintaining the solutionconditions within the metal oxide stability area or co-precipitationstability area so as to produce metal oxides having high loadingcapacities and/or high average oxidation states.
 2. A system for theremoval of pollutants from an aqueous solution comprising a contactoradapted for contacting an aqueous solution containing at least onetarget pollutant with a sorbent, wherein the sorbent removes at least aportion of the target pollutant from the aqueous stream, said sorbentcomprising a metal oxide formed by the process of; a. providing a metalcontaining solution; b. providing a aqueous oxidizing solution, theoxidizing solution being prepared to have Eh and pH values within apolyatomic ion stability area, metal ion stability area, a metal oxidestability area, or a co-precipitation stability area or to move solutionconditions initially into the polyatomic ion stability area, metal ionstability area, metal oxide stability area, or co-precipitationstability area when contacted with the metal containing solution; c.feeding the metal containing solution and the aqueous oxidizing solutioninto at least one continuous flow reactor, the solutions being fedeither separately into the continuous flow reactor where they mix toform a combined mixed processing solution or being premixed and fed as acombined mixed processing solution; d. heating the combined mixedprocessing solution to process temperature; e. monitoring and adjustingcombined mixed processing solution temperature, Eh value, pH value,molarity, and pressure within the continuous flow reactor so as torapidly and adaptively move combined mixed processing solutionconditions into and maintain processing solution conditions within themetal oxide stability area or co-precipitation stability area; and f.maintaining combined mixed processing solution conditions within themetal oxide stability area or co-precipitation stability area as thecombined mixed processing solution travels through the continuous flowreactor so as to produce metal oxides with high loading capacitiesand/or high average oxidation states.
 3. The system of any one of claim1 or 2, wherein the contactor includes a diffuser for creating afluidized bed of sorbent and a clear water overflow for allowing removalof the aqueous stream once at least a portion of a target pollutant hasbeen removed.
 4. The system of any one of claim 1 or 2, wherein thecontactor includes a diffuser for creating a fluidized bed of sorbent, aclear water overflow for allowing removal of the aqueous stream once atleast a portion of a target pollutant has been removed, and a reactedsorbent outlet in the fluidized bed portion of the contactor.
 5. Thesystem of any one of claim 1 or 2, wherein the contactor includes adiffuser for creating a fluidized bed of sorbent, a clear water overflowfor allowing removal of the aqueous stream with at least a portion of atarget pollutant removed, and a recycle stream for controlling velocitythrough the diffuser.
 6. The system of any one of claim 1 or 2, whereinthe contactor is selected from the group consisting of an agitated orstirred vessel, a solid filter element, and a fixed bed of sorbent orcombinations thereof.
 7. The system of any one of claim 1 or 2, whereinthe sorbent is precipitated on an active substrate.
 8. The system of anyone of claim 1 or 2, wherein the sorbent is precipitated on an activesubstrate selected from the group consisting of activated carbon,activated alumina, secondary metal oxide particles.
 9. The system ofclaim 1 or 2, wherein the sorbent is a mixture of a first metal oxideand a second metal oxide that are co-precipitated as the sorbent isbeing produced.
 10. The system of claim 1 or 2, wherein the a foreigncation is introduced in a controlled fashion into the sorbent as thesorbent is being produced.
 11. The system of claim 1 or 2, wherein saidtarget pollutant comprises arsenic, ions of arsenic, or arseniccompounds.
 12. The system of any one of claim 1 or 2, wherein saidtarget pollutant comprises hardness minerals.
 13. The system of any oneof claim 1 or 2, wherein said target pollutant is selected from thegroup consisting of iron, ions of iron, iron compounds, chromium, ionsof chromium, chromium compounds copper, ions of copper, coppercompounds, lead, ions of lead, and lead compounds or combinationsthereof.
 14. The system of any one of claim 1 or 2, wherein said sorbentcomprises oxides of manganese that are defined by the formula MnO_(X),where X is about 1.5 to about 2.0.
 15. The system of claim 1 or 2,wherein said sorbent comprises oxides of manganese that are defined bythe formula MnO_(X), where X is about 1.7 to about 1.95.
 16. The systemof claim 1 or 2, wherein said sorbent comprises oxides of manganese thathave a BET value ranging from about 1 to 1000 m²/gram.
 17. The system ofclaim 1 or 2, wherein said sorbent comprises oxides of manganese thathave a particle size ranging from about 0.5 to about 500 microns.
 18. Ansystem for removal of metals from an aqueous solution, the systemcomprising a contactor formed of a metal oxide containing sorbent;wherein the system is configured to bring the aqueous solution intocontact with the sorbent; wherein said sorbent comprises regenerableoxides of manganese; and wherein said oxides of manganese are defined bythe formula MnO_(X), where X is about 1.5 to about 2.0, have a BET valueranging from about 1 to 1000 m²/gram, and have a particle size rangingfrom about 0.5 to about 500 microns.
 19. The system of claim 17, whereinarsenate and arsenite are removed at removal rates equal to or greaterthan 50%.
 20. The system of claim 17, wherein arsenate and arsenite areremoved at removal rates equal to or greater than 60%.
 21. The system ofclaim 17, wherein arsenate and arsenite are removed at removal ratesequal to or greater than 70%.
 22. The system of claim 17, whereinarsenate and arsenite are removed at removal rates equal to or greaterthan 80%.
 23. The system of claim 17, wherein arsenate and arsenite areremoved at removal rates equal to or greater than 90%.
 24. The system ofclaim 17 wherein arsenate and arsenite are removed at removal ratesequal to or greater than 95%.
 25. The system of claim 17, whereinarsenate and arsenite are removed at removal rates of at least 99%.